switch to xmake for package management (#611)

This change removes our dependency on vcpkg for package management, in favour of bringing some code in-tree in the `thirdparty` folder as well as using the xmake build-in package management feature. For the latter, all the package definitions are maintained in the zen repo itself, in the `repo` folder.

It should now also be easier to build the project as it will no longer depend on having the right version of vcpkg installed, which has been a common problem for new people coming in to the codebase. Now you should only need xmake to build.

* Bumps xmake requirement on github runners to 2.9.9 to resolve an issue where xmake on Windows invokes cmake with `v144` toolchain which does not exist
* BLAKE3 is now in-tree at `thirdparty/blake3`
* cpr is now in-tree at `thirdparty/cpr`
* cxxopts is now in-tree at `thirdparty/cxxopts`
* fmt is now in-tree at `thirdparty/fmt`
* robin-map is now in-tree at `thirdparty/robin-map`
* ryml is now in-tree at `thirdparty/ryml`
* sol2 is now in-tree at `thirdparty/sol2`
* spdlog is now in-tree at `thirdparty/spdlog`
* utfcpp is now in-tree at `thirdparty/utfcpp`
* xmake package repo definitions is in `repo`
* implemented support for sanitizers. ASAN is supported on windows, TSAN, UBSAN, MSAN etc are supported on Linux/MacOS though I have not yet tested it extensively on MacOS
* the zencore encryption implementation also now supports using mbedTLS which is used on MacOS, though for now we still use openssl on Linux
* crashpad
* bumps libcurl to 8.11.0 (from 8.8.0) which should address a rare build upload bug

23 files changed, 14579 insertions, 0 deletions

diff --git a/thirdparty/ryml/src/c4/yml/common.cpp b/thirdparty/ryml/src/c4/yml/common.cpp
new file mode 100644
index 000000000..75b873549
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/common.cpp
@@ -0,0 +1,117 @@
+#include "c4/yml/common.hpp"
+
+#ifndef RYML_NO_DEFAULT_CALLBACKS
+#   include <stdlib.h>
+#   include <stdio.h>
+#endif // RYML_NO_DEFAULT_CALLBACKS
+
+namespace c4 {
+namespace yml {
+
+namespace {
+Callbacks s_default_callbacks;
+} // anon namespace
+
+#ifndef RYML_NO_DEFAULT_CALLBACKS
+void report_error_impl(const char* msg, size_t length, Location loc, FILE *f)
+{
+    if(!f)
+        f = stderr;
+    if(loc)
+    {
+        if(!loc.name.empty())
+        {
+            fwrite(loc.name.str, 1, loc.name.len, f);
+            fputc(':', f);
+        }
+        fprintf(f, "%zu:", loc.line);
+        if(loc.col)
+            fprintf(f, "%zu:", loc.col);
+        if(loc.offset)
+            fprintf(f, " (%zuB):", loc.offset);
+    }
+    fprintf(f, "%.*s\n", (int)length, msg);
+    fflush(f);
+}
+
+void error_impl(const char* msg, size_t length, Location loc, void * /*user_data*/)
+{
+    report_error_impl(msg, length, loc, nullptr);
+    ::abort();
+}
+
+void* allocate_impl(size_t length, void * /*hint*/, void * /*user_data*/)
+{
+    void *mem = ::malloc(length);
+    if(mem == nullptr)
+    {
+        const char msg[] = "could not allocate memory";
+        error_impl(msg, sizeof(msg)-1, {}, nullptr);
+    }
+    return mem;
+}
+
+void free_impl(void *mem, size_t /*length*/, void * /*user_data*/)
+{
+    ::free(mem);
+}
+#endif // RYML_NO_DEFAULT_CALLBACKS
+
+
+
+Callbacks::Callbacks()
+    :
+    m_user_data(nullptr),
+    #ifndef RYML_NO_DEFAULT_CALLBACKS
+    m_allocate(allocate_impl),
+    m_free(free_impl),
+    m_error(error_impl)
+    #else
+    m_allocate(nullptr),
+    m_free(nullptr),
+    m_error(nullptr)
+    #endif
+{
+}
+
+Callbacks::Callbacks(void *user_data, pfn_allocate alloc_, pfn_free free_, pfn_error error_)
+    :
+    m_user_data(user_data),
+    #ifndef RYML_NO_DEFAULT_CALLBACKS
+    m_allocate(alloc_ ? alloc_ : allocate_impl),
+    m_free(free_ ? free_ : free_impl),
+    m_error(error_ ? error_ : error_impl)
+    #else
+    m_allocate(alloc_),
+    m_free(free_),
+    m_error(error_)
+    #endif
+{
+    C4_CHECK(m_allocate);
+    C4_CHECK(m_free);
+    C4_CHECK(m_error);
+}
+
+
+void set_callbacks(Callbacks const& c)
+{
+    s_default_callbacks = c;
+}
+
+Callbacks const& get_callbacks()
+{
+    return s_default_callbacks;
+}
+
+void reset_callbacks()
+{
+    set_callbacks(Callbacks());
+}
+
+void error(const char *msg, size_t msg_len, Location loc)
+{
+    s_default_callbacks.m_error(msg, msg_len, loc, s_default_callbacks.m_user_data);
+}
+
+} // namespace yml
+} // namespace c4
diff --git a/thirdparty/ryml/src/c4/yml/common.hpp b/thirdparty/ryml/src/c4/yml/common.hpp
new file mode 100644
index 000000000..21aef6ba2
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/common.hpp
@@ -0,0 +1,278 @@
+#ifndef _C4_YML_COMMON_HPP_
+#define _C4_YML_COMMON_HPP_
+
+#include <cstddef>
+#include <c4/substr.hpp>
+#include <c4/yml/export.hpp>
+
+
+#ifndef RYML_USE_ASSERT
+#   define RYML_USE_ASSERT C4_USE_ASSERT
+#endif
+
+
+#if RYML_USE_ASSERT
+#   define RYML_ASSERT(cond) RYML_CHECK(cond)
+#   define RYML_ASSERT_MSG(cond, msg) RYML_CHECK_MSG(cond, msg)
+#else
+#   define RYML_ASSERT(cond)
+#   define RYML_ASSERT_MSG(cond, msg)
+#endif
+
+
+#if defined(NDEBUG) || defined(C4_NO_DEBUG_BREAK)
+#   define RYML_DEBUG_BREAK()
+#else
+#   define RYML_DEBUG_BREAK()                               \
+    {                                                       \
+        if(c4::get_error_flags() & c4::ON_ERROR_DEBUGBREAK) \
+        {                                                   \
+            C4_DEBUG_BREAK();                               \
+        }                                                   \
+    }
+#endif
+
+
+#define RYML_CHECK(cond)                                                \
+    do {                                                                \
+        if(!(cond))                                                     \
+        {                                                               \
+            RYML_DEBUG_BREAK()                                          \
+            c4::yml::error("check failed: " #cond, c4::yml::Location(__FILE__, __LINE__, 0)); \
+        }                                                               \
+    } while(0)
+
+#define RYML_CHECK_MSG(cond, msg)                                       \
+    do                                                                  \
+    {                                                                   \
+        if(!(cond))                                                     \
+        {                                                               \
+            RYML_DEBUG_BREAK()                                          \
+            c4::yml::error(msg ": check failed: " #cond, c4::yml::Location(__FILE__, __LINE__, 0)); \
+        }                                                               \
+    } while(0)
+
+
+#if C4_CPP >= 14
+#   define RYML_DEPRECATED(msg) [[deprecated(msg)]]
+#else
+#   if defined(_MSC_VER)
+#       define RYML_DEPRECATED(msg) __declspec(deprecated(msg))
+#   else // defined(__GNUC__) || defined(__clang__)
+#       define RYML_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#   endif
+#endif
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+namespace c4 {
+namespace yml {
+
+enum : size_t {
+    /** a null position */
+    npos = size_t(-1),
+    /** an index to none */
+    NONE = size_t(-1)
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+//! holds a position into a source buffer
+struct RYML_EXPORT LineCol
+{
+    //! number of bytes from the beginning of the source buffer
+    size_t offset;
+    //! line
+    size_t line;
+    //! column
+    size_t col;
+
+    LineCol() : offset(), line(), col() {}
+    //! construct from line and column
+    LineCol(size_t l, size_t c) : offset(0), line(l), col(c) {}
+    //! construct from offset, line and column
+    LineCol(size_t o, size_t l, size_t c) : offset(o), line(l), col(c) {}
+};
+
+
+//! a source file position
+struct RYML_EXPORT Location : public LineCol
+{
+    csubstr name;
+
+    operator bool () const { return !name.empty() || line != 0 || offset != 0; }
+
+    Location() : LineCol(), name() {}
+    Location(                         size_t l, size_t c) : LineCol{   l, c}, name( ) {}
+    Location(    csubstr n,           size_t l, size_t c) : LineCol{   l, c}, name(n) {}
+    Location(    csubstr n, size_t b, size_t l, size_t c) : LineCol{b, l, c}, name(n) {}
+    Location(const char *n,           size_t l, size_t c) : LineCol{   l, c}, name(to_csubstr(n)) {}
+    Location(const char *n, size_t b, size_t l, size_t c) : LineCol{b, l, c}, name(to_csubstr(n)) {}
+};
+
+
+//-----------------------------------------------------------------------------
+
+/** the type of the function used to report errors. This function must
+ * interrupt execution, either by raising an exception or calling
+ * std::abort().
+ *
+ * @warning the error callback must never return: it must either abort
+ * or throw an exception. Otherwise, the parser will enter into an
+ * infinite loop, or the program may crash. */
+using pfn_error = void (*)(const char* msg, size_t msg_len, Location location, void *user_data);
+/** the type of the function used to allocate memory */
+using pfn_allocate = void* (*)(size_t len, void* hint, void *user_data);
+/** the type of the function used to free memory */
+using pfn_free = void (*)(void* mem, size_t size, void *user_data);
+
+/** trigger an error: call the current error callback. */
+RYML_EXPORT void error(const char *msg, size_t msg_len, Location loc);
+/** @overload error */
+inline void error(const char *msg, size_t msg_len)
+{
+    error(msg, msg_len, Location{});
+}
+/** @overload error */
+template<size_t N>
+inline void error(const char (&msg)[N], Location loc)
+{
+    error(msg, N-1, loc);
+}
+/** @overload error */
+template<size_t N>
+inline void error(const char (&msg)[N])
+{
+    error(msg, N-1, Location{});
+}
+
+//-----------------------------------------------------------------------------
+
+/** a c-style callbacks class
+ *
+ * @warning the error callback must never return: it must either abort
+ * or throw an exception. Otherwise, the parser will enter into an
+ * infinite loop, or the program may crash. */
+struct RYML_EXPORT Callbacks
+{
+    void *       m_user_data;
+    pfn_allocate m_allocate;
+    pfn_free     m_free;
+    pfn_error    m_error;
+
+    Callbacks();
+    Callbacks(void *user_data, pfn_allocate alloc, pfn_free free, pfn_error error_);
+
+    bool operator!= (Callbacks const& that) const { return !operator==(that); }
+    bool operator== (Callbacks const& that) const
+    {
+        return (m_user_data == that.m_user_data &&
+                m_allocate == that.m_allocate &&
+                m_free == that.m_free &&
+                m_error == that.m_error);
+    }
+};
+
+/** set the global callbacks.
+ *
+ * @warning the error callback must never return: it must either abort
+ * or throw an exception. Otherwise, the parser will enter into an
+ * infinite loop, or the program may crash. */
+RYML_EXPORT void set_callbacks(Callbacks const& c);
+/// get the global callbacks
+RYML_EXPORT Callbacks const& get_callbacks();
+/// set the global callbacks back to their defaults
+RYML_EXPORT void reset_callbacks();
+
+/// @cond dev
+#define _RYML_CB_ERR(cb, msg_literal)                                   \
+do                                                                      \
+{                                                                       \
+    const char msg[] = msg_literal;                                     \
+    RYML_DEBUG_BREAK()                                                  \
+    (cb).m_error(msg, sizeof(msg), c4::yml::Location(__FILE__, 0, __LINE__, 0), (cb).m_user_data); \
+} while(0)
+#define _RYML_CB_CHECK(cb, cond)                                        \
+    do                                                                  \
+    {                                                                   \
+        if(!(cond))                                                     \
+        {                                                               \
+            const char msg[] = "check failed: " #cond;                  \
+            RYML_DEBUG_BREAK()                                          \
+            (cb).m_error(msg, sizeof(msg), c4::yml::Location(__FILE__, 0, __LINE__, 0), (cb).m_user_data); \
+        }                                                               \
+    } while(0)
+#ifdef RYML_USE_ASSERT
+#define _RYML_CB_ASSERT(cb, cond) _RYML_CB_CHECK((cb), (cond))
+#else
+#define _RYML_CB_ASSERT(cb, cond) do {} while(0)
+#endif
+#define _RYML_CB_ALLOC_HINT(cb, T, num, hint) (T*) (cb).m_allocate((num) * sizeof(T), (hint), (cb).m_user_data)
+#define _RYML_CB_ALLOC(cb, T, num) _RYML_CB_ALLOC_HINT((cb), (T), (num), nullptr)
+#define _RYML_CB_FREE(cb, buf, T, num)                              \
+    do {                                                            \
+        (cb).m_free((buf), (num) * sizeof(T), (cb).m_user_data);    \
+        (buf) = nullptr;                                            \
+    } while(0)
+
+
+
+namespace detail {
+template<int8_t signedval, uint8_t unsignedval>
+struct _charconstant_t
+    : public std::conditional<std::is_signed<char>::value,
+                              std::integral_constant<int8_t, signedval>,
+                              std::integral_constant<uint8_t, unsignedval>>::type
+{};
+#define _RYML_CHCONST(signedval, unsignedval) ::c4::yml::detail::_charconstant_t<INT8_C(signedval), UINT8_C(unsignedval)>::value
+} // namespace detail
+
+
+namespace detail {
+struct _SubstrWriter
+{
+    substr buf;
+    size_t pos;
+    _SubstrWriter(substr buf_, size_t pos_=0) : buf(buf_), pos(pos_) {}
+    void append(csubstr s)
+    {
+        C4_ASSERT(!s.overlaps(buf));
+        if(pos + s.len <= buf.len)
+            memcpy(buf.str + pos, s.str, s.len);
+        pos += s.len;
+    }
+    void append(char c)
+    {
+        if(pos < buf.len)
+            buf.str[pos] = c;
+        ++pos;
+    }
+    void append_n(char c, size_t numtimes)
+    {
+        if(pos + numtimes < buf.len)
+            memset(buf.str + pos, c, numtimes);
+        pos += numtimes;
+    }
+    size_t slack() const { return pos <= buf.len ? buf.len - pos : 0; }
+    size_t excess() const { return pos > buf.len ? pos - buf.len : 0; }
+    //! get the part written so far
+    csubstr curr() const { return pos <= buf.len ? buf.first(pos) : buf; }
+    //! get the part that is still free to write to (the remainder)
+    substr rem() { return pos < buf.len ? buf.sub(pos) : buf.last(0); }
+
+    size_t advance(size_t more) { pos += more; return pos; }
+};
+} // namespace detail
+
+/// @endcond
+
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_COMMON_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/checks.hpp b/thirdparty/ryml/src/c4/yml/detail/checks.hpp
new file mode 100644
index 000000000..39b49e856
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/checks.hpp
@@ -0,0 +1,200 @@
+#ifndef C4_YML_DETAIL_CHECKS_HPP_
+#define C4_YML_DETAIL_CHECKS_HPP_
+
+#include "c4/yml/tree.hpp"
+
+#ifdef __clang__
+#   pragma clang diagnostic push
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wtype-limits" // error: comparison of unsigned expression >= 0 is always true
+#elif defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4296/*expression is always 'boolean_value'*/)
+#endif
+
+namespace c4 {
+namespace yml {
+
+
+void check_invariants(Tree const& t, size_t node=NONE);
+void check_free_list(Tree const& t);
+void check_arena(Tree const& t);
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_invariants(Tree const& t, size_t node)
+{
+    if(node == NONE)
+    {
+        if(t.size() == 0) return;
+        node = t.root_id();
+    }
+
+    auto const& n = *t._p(node);
+#ifdef RYML_DBG
+    if(n.m_first_child != NONE || n.m_last_child != NONE)
+    {
+        printf("check(%zu): fc=%zu lc=%zu\n", node, n.m_first_child, n.m_last_child);
+    }
+    else
+    {
+        printf("check(%zu)\n", node);
+    }
+#endif
+
+    C4_CHECK(n.m_parent != node);
+    if(n.m_parent == NONE)
+    {
+        C4_CHECK(t.is_root(node));
+    }
+    else //if(n.m_parent != NONE)
+    {
+        C4_CHECK(t.has_child(n.m_parent, node));
+
+        auto const& p = *t._p(n.m_parent);
+        if(n.m_prev_sibling == NONE)
+        {
+            C4_CHECK(p.m_first_child == node);
+            C4_CHECK(t.first_sibling(node) == node);
+        }
+        else
+        {
+            C4_CHECK(p.m_first_child != node);
+            C4_CHECK(t.first_sibling(node) != node);
+        }
+
+        if(n.m_next_sibling == NONE)
+        {
+            C4_CHECK(p.m_last_child == node);
+            C4_CHECK(t.last_sibling(node) == node);
+        }
+        else
+        {
+            C4_CHECK(p.m_last_child != node);
+            C4_CHECK(t.last_sibling(node) != node);
+        }
+    }
+
+    C4_CHECK(n.m_first_child != node);
+    C4_CHECK(n.m_last_child != node);
+    if(n.m_first_child != NONE || n.m_last_child != NONE)
+    {
+        C4_CHECK(n.m_first_child != NONE);
+        C4_CHECK(n.m_last_child != NONE);
+    }
+
+    C4_CHECK(n.m_prev_sibling != node);
+    C4_CHECK(n.m_next_sibling != node);
+    if(n.m_prev_sibling != NONE)
+    {
+        C4_CHECK(t._p(n.m_prev_sibling)->m_next_sibling == node);
+        C4_CHECK(t._p(n.m_prev_sibling)->m_prev_sibling != node);
+    }
+    if(n.m_next_sibling != NONE)
+    {
+        C4_CHECK(t._p(n.m_next_sibling)->m_prev_sibling == node);
+        C4_CHECK(t._p(n.m_next_sibling)->m_next_sibling != node);
+    }
+
+    size_t count = 0;
+    for(size_t i = n.m_first_child; i != NONE; i = t.next_sibling(i))
+    {
+#ifdef RYML_DBG
+        printf("check(%zu):               descend to child[%zu]=%zu\n", node, count, i);
+#endif
+        auto const& ch = *t._p(i);
+        C4_CHECK(ch.m_parent == node);
+        C4_CHECK(ch.m_next_sibling != i);
+        ++count;
+    }
+    C4_CHECK(count == t.num_children(node));
+
+    if(n.m_prev_sibling == NONE && n.m_next_sibling == NONE)
+    {
+        if(n.m_parent != NONE)
+        {
+            C4_CHECK(t.num_children(n.m_parent) == 1);
+            C4_CHECK(t.num_siblings(node) == 1);
+        }
+    }
+
+    if(node == t.root_id())
+    {
+        C4_CHECK(t.size() == t.m_size);
+        C4_CHECK(t.capacity() == t.m_cap);
+        C4_CHECK(t.m_cap == t.m_size + t.slack());
+        check_free_list(t);
+        check_arena(t);
+    }
+
+    for(size_t i = t.first_child(node); i != NONE; i = t.next_sibling(i))
+    {
+        check_invariants(t, i);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_free_list(Tree const& t)
+{
+    if(t.m_free_head == NONE)
+    {
+        C4_CHECK(t.m_free_tail == t.m_free_head);
+        return;
+    }
+
+    C4_CHECK(t.m_free_head >= 0 && t.m_free_head < t.m_cap);
+    C4_CHECK(t.m_free_tail >= 0 && t.m_free_tail < t.m_cap);
+
+    auto const& head = *t._p(t.m_free_head);
+    //auto const& tail = *t._p(t.m_free_tail);
+
+    //C4_CHECK(head.m_prev_sibling == NONE);
+    //C4_CHECK(tail.m_next_sibling == NONE);
+
+    size_t count = 0;
+    for(size_t i = t.m_free_head, prev = NONE; i != NONE; i = t._p(i)->m_next_sibling)
+    {
+        auto const& elm = *t._p(i);
+        if(&elm != &head)
+        {
+            C4_CHECK(elm.m_prev_sibling == prev);
+        }
+        prev = i;
+        ++count;
+    }
+    C4_CHECK(count == t.slack());
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void check_arena(Tree const& t)
+{
+    C4_CHECK(t.m_arena.len == 0 || (t.m_arena_pos >= 0 && t.m_arena_pos <= t.m_arena.len));
+    C4_CHECK(t.arena_size() == t.m_arena_pos);
+    C4_CHECK(t.arena_slack() + t.m_arena_pos == t.m_arena.len);
+}
+
+
+} /* namespace yml */
+} /* namespace c4 */
+
+#ifdef __clang__
+#   pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic pop
+#elif defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+#endif /* C4_YML_DETAIL_CHECKS_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp b/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp
new file mode 100644
index 000000000..457f1700d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/parser_dbg.hpp
@@ -0,0 +1,137 @@
+#ifndef _C4_YML_DETAIL_PARSER_DBG_HPP_
+#define _C4_YML_DETAIL_PARSER_DBG_HPP_
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "../common.hpp"
+#endif
+#include <cstdio>
+
+//-----------------------------------------------------------------------------
+// some debugging scaffolds
+
+#if defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4068/*unknown pragma*/)
+#endif
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunknown-pragmas"
+//#pragma GCC diagnostic ignored "-Wpragma-system-header-outside-header"
+#pragma GCC system_header
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Werror"
+#pragma clang diagnostic ignored "-Wgnu-zero-variadic-macro-arguments"
+
+// some debugging scaffolds
+#ifdef RYML_DBG
+#include <c4/dump.hpp>
+namespace c4 {
+inline void _dbg_dumper(csubstr s) { fwrite(s.str, 1, s.len, stdout); };
+template<class ...Args>
+void _dbg_printf(c4::csubstr fmt, Args&& ...args)
+{
+    static char writebuf[256];
+    auto results = c4::format_dump_resume<&_dbg_dumper>(writebuf, fmt, std::forward<Args>(args)...);
+    // resume writing if the results failed to fit the buffer
+    if(C4_UNLIKELY(results.bufsize > sizeof(writebuf))) // bufsize will be that of the largest element serialized. Eg int(1), will require 1 byte.
+    {
+        results = format_dump_resume<&_dbg_dumper>(results, writebuf, fmt, std::forward<Args>(args)...);
+        if(C4_UNLIKELY(results.bufsize > sizeof(writebuf)))
+        {
+            results = format_dump_resume<&_dbg_dumper>(results, writebuf, fmt, std::forward<Args>(args)...);
+        }
+    }
+}
+} // namespace c4
+
+#   define _c4dbgt(fmt, ...)   this->_dbg ("{}:{}: "   fmt     , __FILE__, __LINE__, ## __VA_ARGS__)
+#   define _c4dbgpf(fmt, ...)  _dbg_printf("{}:{}: "   fmt "\n", __FILE__, __LINE__, ## __VA_ARGS__)
+#   define _c4dbgp(msg)        _dbg_printf("{}:{}: "   msg "\n", __FILE__, __LINE__                )
+#   define _c4dbgq(msg)        _dbg_printf(msg "\n")
+#   define _c4err(fmt, ...)   \
+    do { if(c4::is_debugger_attached()) { C4_DEBUG_BREAK(); } \
+         this->_err("ERROR:\n" "{}:{}: " fmt, __FILE__, __LINE__, ## __VA_ARGS__); } while(0)
+#else
+#   define _c4dbgt(fmt, ...)
+#   define _c4dbgpf(fmt, ...)
+#   define _c4dbgp(msg)
+#   define _c4dbgq(msg)
+#   define _c4err(fmt, ...)   \
+    do { if(c4::is_debugger_attached()) { C4_DEBUG_BREAK(); } \
+         this->_err("ERROR: " fmt, ## __VA_ARGS__); } while(0)
+#endif
+
+#define _c4prsp(sp) sp
+#define _c4presc(s) __c4presc(s.str, s.len)
+inline c4::csubstr _c4prc(const char &C4_RESTRICT c)
+{
+    switch(c)
+    {
+    case '\n': return c4::csubstr("\\n");
+    case '\t': return c4::csubstr("\\t");
+    case '\0': return c4::csubstr("\\0");
+    case '\r': return c4::csubstr("\\r");
+    case '\f': return c4::csubstr("\\f");
+    case '\b': return c4::csubstr("\\b");
+    case '\v': return c4::csubstr("\\v");
+    case '\a': return c4::csubstr("\\a");
+    default: return c4::csubstr(&c, 1);
+    }
+}
+inline void __c4presc(const char *s, size_t len)
+{
+    size_t prev = 0;
+    for(size_t i = 0; i < len; ++i)
+    {
+        switch(s[i])
+        {
+        case '\n'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('n'); putchar('\n'); prev = i+1; break;
+        case '\t'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('t'); prev = i+1; break;
+        case '\0'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('0'); prev = i+1; break;
+        case '\r'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('r'); prev = i+1; break;
+        case '\f'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('f'); prev = i+1; break;
+        case '\b'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('b'); prev = i+1; break;
+        case '\v'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('v'); prev = i+1; break;
+        case '\a'  : fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('a'); prev = i+1; break;
+        case '\x1b': fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('e'); prev = i+1; break;
+        case -0x3e/*0xc2u*/:
+            if(i+1 < len)
+            {
+                if(s[i+1] == -0x60/*0xa0u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('_'); prev = i+2; ++i;
+                }
+                else if(s[i+1] == -0x7b/*0x85u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('N'); prev = i+2; ++i;
+                }
+                break;
+            }
+        case -0x1e/*0xe2u*/:
+            if(i+2 < len && s[i+1] == -0x80/*0x80u*/)
+            {
+                if(s[i+2] == -0x58/*0xa8u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('L'); prev = i+3; i += 2;
+                }
+                else if(s[i+2] == -0x57/*0xa9u*/)
+                {
+                    fwrite(s+prev, 1, i-prev, stdout); putchar('\\'); putchar('P'); prev = i+3; i += 2;
+                }
+                break;
+            }
+        }
+    }
+    fwrite(s + prev, 1, len - prev, stdout);
+}
+
+#pragma clang diagnostic pop
+#pragma GCC diagnostic pop
+
+#if defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+
+#endif /* _C4_YML_DETAIL_PARSER_DBG_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/print.hpp b/thirdparty/ryml/src/c4/yml/detail/print.hpp
new file mode 100644
index 000000000..f88dc251d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/print.hpp
@@ -0,0 +1,128 @@
+#ifndef C4_YML_DETAIL_PRINT_HPP_
+#define C4_YML_DETAIL_PRINT_HPP_
+
+#include "c4/yml/tree.hpp"
+#include "c4/yml/node.hpp"
+
+
+namespace c4 {
+namespace yml {
+
+
+inline size_t print_node(Tree const& p, size_t node, int level, size_t count, bool print_children)
+{
+    printf("[%zd]%*s[%zd] %p", count, (2*level), "", node, (void*)p.get(node));
+    if(p.is_root(node))
+    {
+        printf(" [ROOT]");
+    }
+    printf(" %s:", p.type_str(node));
+    if(p.has_key(node))
+    {
+        if(p.has_key_anchor(node))
+        {
+            csubstr ka = p.key_anchor(node);
+            printf(" &%.*s", (int)ka.len, ka.str);
+        }
+        if(p.has_key_tag(node))
+        {
+            csubstr kt = p.key_tag(node);
+            csubstr k  = p.key(node);
+            printf(" %.*s '%.*s'", (int)kt.len, kt.str, (int)k.len, k.str);
+        }
+        else
+        {
+            csubstr k  = p.key(node);
+            printf(" '%.*s'", (int)k.len, k.str);
+        }
+    }
+    else
+    {
+        RYML_ASSERT( ! p.has_key_tag(node));
+    }
+    if(p.has_val(node))
+    {
+        if(p.has_val_tag(node))
+        {
+            csubstr vt = p.val_tag(node);
+            csubstr v  = p.val(node);
+            printf(" %.*s '%.*s'", (int)vt.len, vt.str, (int)v.len, v.str);
+        }
+        else
+        {
+            csubstr v  = p.val(node);
+            printf(" '%.*s'", (int)v.len, v.str);
+        }
+    }
+    else
+    {
+        if(p.has_val_tag(node))
+        {
+            csubstr vt = p.val_tag(node);
+            printf(" %.*s", (int)vt.len, vt.str);
+        }
+    }
+    if(p.has_val_anchor(node))
+    {
+        auto &a = p.val_anchor(node);
+        printf(" valanchor='&%.*s'", (int)a.len, a.str);
+    }
+    printf(" (%zd sibs)", p.num_siblings(node));
+
+    ++count;
+
+    if(p.is_container(node))
+    {
+        printf(" %zd children:\n", p.num_children(node));
+        if(print_children)
+        {
+            for(size_t i = p.first_child(node); i != NONE; i = p.next_sibling(i))
+            {
+                count = print_node(p, i, level+1, count, print_children);
+            }
+        }
+    }
+    else
+    {
+        printf("\n");
+    }
+
+    return count;
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline void print_node(ConstNodeRef const& p, int level=0)
+{
+    print_node(*p.tree(), p.id(), level, 0, true);
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+inline size_t print_tree(Tree const& p, size_t node=NONE)
+{
+    printf("--------------------------------------\n");
+    size_t ret = 0;
+    if(!p.empty())
+    {
+        if(node == NONE)
+            node = p.root_id();
+        ret = print_node(p, node, 0, 0, true);
+    }
+    printf("#nodes=%zd vs #printed=%zd\n", p.size(), ret);
+    printf("--------------------------------------\n");
+    return ret;
+}
+
+
+} /* namespace yml */
+} /* namespace c4 */
+
+
+#endif /* C4_YML_DETAIL_PRINT_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/detail/stack.hpp b/thirdparty/ryml/src/c4/yml/detail/stack.hpp
new file mode 100644
index 000000000..95677ae27
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/detail/stack.hpp
@@ -0,0 +1,274 @@
+#ifndef _C4_YML_DETAIL_STACK_HPP_
+#define _C4_YML_DETAIL_STACK_HPP_
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "../common.hpp"
+#endif
+
+#ifdef RYML_DBG
+#   include <type_traits>
+#endif
+
+#include <string.h>
+
+namespace c4 {
+namespace yml {
+namespace detail {
+
+/** A lightweight contiguous stack with SSO. This avoids a dependency on std. */
+template<class T, size_t N=16>
+class stack
+{
+    static_assert(std::is_trivially_copyable<T>::value, "T must be trivially copyable");
+    static_assert(std::is_trivially_destructible<T>::value, "T must be trivially destructible");
+
+    enum : size_t { sso_size = N };
+
+public:
+
+    T         m_buf[N];
+    T *       m_stack;
+    size_t    m_size;
+    size_t    m_capacity;
+    Callbacks m_callbacks;
+
+public:
+
+    constexpr static bool is_contiguous() { return true; }
+
+    stack(Callbacks const& cb)
+        : m_buf()
+        , m_stack(m_buf)
+        , m_size(0)
+        , m_capacity(N)
+        , m_callbacks(cb) {}
+    stack() : stack(get_callbacks()) {}
+    ~stack()
+    {
+        _free();
+    }
+
+    stack(stack const& that) noexcept : stack(that.m_callbacks)
+    {
+        resize(that.m_size);
+        _cp(&that);
+    }
+
+    stack(stack &&that) noexcept : stack(that.m_callbacks)
+    {
+        _mv(&that);
+    }
+
+    stack& operator= (stack const& that) noexcept
+    {
+        _cb(that.m_callbacks);
+        resize(that.m_size);
+        _cp(&that);
+        return *this;
+    }
+
+    stack& operator= (stack &&that) noexcept
+    {
+        _cb(that.m_callbacks);
+        _mv(&that);
+        return *this;
+    }
+
+public:
+
+    size_t size() const { return m_size; }
+    size_t empty() const { return m_size == 0; }
+    size_t capacity() const { return m_capacity; }
+
+    void clear()
+    {
+        m_size = 0;
+    }
+
+    void resize(size_t sz)
+    {
+        reserve(sz);
+        m_size = sz;
+    }
+
+    void reserve(size_t sz);
+
+    void push(T const& C4_RESTRICT n)
+    {
+        RYML_ASSERT((const char*)&n + sizeof(T) < (const char*)m_stack || &n > m_stack + m_capacity);
+        if(m_size == m_capacity)
+        {
+            size_t cap = m_capacity == 0 ? N : 2 * m_capacity;
+            reserve(cap);
+        }
+        m_stack[m_size] = n;
+        ++m_size;
+    }
+
+    void push_top()
+    {
+        RYML_ASSERT(m_size > 0);
+        if(m_size == m_capacity)
+        {
+            size_t cap = m_capacity == 0 ? N : 2 * m_capacity;
+            reserve(cap);
+        }
+        m_stack[m_size] = m_stack[m_size - 1];
+        ++m_size;
+    }
+
+    T const& C4_RESTRICT pop()
+    {
+        RYML_ASSERT(m_size > 0);
+        --m_size;
+        return m_stack[m_size];
+    }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT top() const { RYML_ASSERT(m_size > 0); return m_stack[m_size - 1]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT top()       { RYML_ASSERT(m_size > 0); return m_stack[m_size - 1]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT bottom() const { RYML_ASSERT(m_size > 0); return m_stack[0]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT bottom()       { RYML_ASSERT(m_size > 0); return m_stack[0]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT top(size_t i) const { RYML_ASSERT(i < m_size); return m_stack[m_size - 1 - i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT top(size_t i)       { RYML_ASSERT(i < m_size); return m_stack[m_size - 1 - i]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT bottom(size_t i) const { RYML_ASSERT(i < m_size); return m_stack[i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT bottom(size_t i)       { RYML_ASSERT(i < m_size); return m_stack[i]; }
+
+    C4_ALWAYS_INLINE T const& C4_RESTRICT operator[](size_t i) const { RYML_ASSERT(i < m_size); return m_stack[i]; }
+    C4_ALWAYS_INLINE T      & C4_RESTRICT operator[](size_t i)       { RYML_ASSERT(i < m_size); return m_stack[i]; }
+
+public:
+
+    using       iterator = T       *;
+    using const_iterator = T const *;
+
+    iterator begin() { return m_stack; }
+    iterator end  () { return m_stack + m_size; }
+
+    const_iterator begin() const { return (const_iterator)m_stack; }
+    const_iterator end  () const { return (const_iterator)m_stack + m_size; }
+
+public:
+    void _free();
+    void _cp(stack const* C4_RESTRICT that);
+    void _mv(stack * that);
+    void _cb(Callbacks const& cb);
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::reserve(size_t sz)
+{
+    if(sz <= m_size)
+        return;
+    if(sz <= N)
+    {
+        m_stack = m_buf;
+        m_capacity = N;
+        return;
+    }
+    T *buf = (T*) m_callbacks.m_allocate(sz * sizeof(T), m_stack, m_callbacks.m_user_data);
+    memcpy(buf, m_stack, m_size * sizeof(T));
+    if(m_stack != m_buf)
+    {
+        m_callbacks.m_free(m_stack, m_capacity * sizeof(T), m_callbacks.m_user_data);
+    }
+    m_stack = buf;
+    m_capacity = sz;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_free()
+{
+    RYML_ASSERT(m_stack != nullptr); // this structure cannot be memset() to zero
+    if(m_stack != m_buf)
+    {
+        m_callbacks.m_free(m_stack, m_capacity * sizeof(T), m_callbacks.m_user_data);
+        m_stack = m_buf;
+        m_size = N;
+        m_capacity = N;
+    }
+    else
+    {
+        RYML_ASSERT(m_capacity == N);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_cp(stack const* C4_RESTRICT that)
+{
+    if(that->m_stack != that->m_buf)
+    {
+        RYML_ASSERT(that->m_capacity > N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+    }
+    else
+    {
+        RYML_ASSERT(that->m_capacity <= N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+    }
+    memcpy(m_stack, that->m_stack, that->m_size * sizeof(T));
+    m_size = that->m_size;
+    m_capacity = that->m_size < N ? N : that->m_size;
+    m_callbacks = that->m_callbacks;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_mv(stack * that)
+{
+    if(that->m_stack != that->m_buf)
+    {
+        RYML_ASSERT(that->m_capacity > N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+        m_stack = that->m_stack;
+    }
+    else
+    {
+        RYML_ASSERT(that->m_capacity <= N);
+        RYML_ASSERT(that->m_size <= that->m_capacity);
+        memcpy(m_buf, that->m_buf, that->m_size * sizeof(T));
+        m_stack = m_buf;
+    }
+    m_size = that->m_size;
+    m_capacity = that->m_capacity;
+    m_callbacks = that->m_callbacks;
+    // make sure no deallocation happens on destruction
+    RYML_ASSERT(that->m_stack != m_buf);
+    that->m_stack = that->m_buf;
+    that->m_capacity = N;
+    that->m_size = 0;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T, size_t N>
+void stack<T, N>::_cb(Callbacks const& cb)
+{
+    if(cb != m_callbacks)
+    {
+        _free();
+        m_callbacks = cb;
+    }
+}
+
+} // namespace detail
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_DETAIL_STACK_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/emit.def.hpp b/thirdparty/ryml/src/c4/yml/emit.def.hpp
new file mode 100644
index 000000000..d262a9e2a
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/emit.def.hpp
@@ -0,0 +1,960 @@
+#ifndef _C4_YML_EMIT_DEF_HPP_
+#define _C4_YML_EMIT_DEF_HPP_
+
+#ifndef _C4_YML_EMIT_HPP_
+#include "c4/yml/emit.hpp"
+#endif
+
+namespace c4 {
+namespace yml {
+
+template<class Writer>
+substr Emitter<Writer>::emit_as(EmitType_e type, Tree const& t, size_t id, bool error_on_excess)
+{
+    if(t.empty())
+    {
+        _RYML_CB_ASSERT(t.callbacks(), id == NONE);
+        return {};
+    }
+    _RYML_CB_CHECK(t.callbacks(), id < t.size());
+    m_tree = &t;
+    if(type == EMIT_YAML)
+        _emit_yaml(id);
+    else if(type == EMIT_JSON)
+        _do_visit_json(id);
+    else
+        _RYML_CB_ERR(m_tree->callbacks(), "unknown emit type");
+    return this->Writer::_get(error_on_excess);
+}
+
+template<class Writer>
+substr Emitter<Writer>::emit_as(EmitType_e type, Tree const& t, bool error_on_excess)
+{
+    if(t.empty())
+        return {};
+    return this->emit_as(type, t, t.root_id(), error_on_excess);
+}
+
+template<class Writer>
+substr Emitter<Writer>::emit_as(EmitType_e type, ConstNodeRef const& n, bool error_on_excess)
+{
+    _RYML_CB_CHECK(n.tree()->callbacks(), n.valid());
+    return this->emit_as(type, *n.tree(), n.id(), error_on_excess);
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class Writer>
+void Emitter<Writer>::_emit_yaml(size_t id)
+{
+    // save branches in the visitor by doing the initial stream/doc
+    // logic here, sparing the need to check stream/val/keyval inside
+    // the visitor functions
+    auto dispatch = [this](size_t node){
+        NodeType ty = m_tree->type(node);
+        if(ty.marked_flow_sl())
+            _do_visit_flow_sl(node, 0);
+        else if(ty.marked_flow_ml())
+            _do_visit_flow_ml(node, 0);
+        else
+        {
+            _do_visit_block(node, 0);
+        }
+    };
+    if(!m_tree->is_root(id))
+    {
+        if(m_tree->is_container(id) && !m_tree->type(id).marked_flow())
+        {
+            size_t ilevel = 0;
+            if(m_tree->has_key(id))
+            {
+                this->Writer::_do_write(m_tree->key(id));
+                this->Writer::_do_write(":\n");
+                ++ilevel;
+            }
+            _do_visit_block_container(id, ilevel, ilevel);
+            return;
+        }
+    }
+
+    auto *btd = m_tree->tag_directives().b;
+    auto *etd = m_tree->tag_directives().e;
+    auto write_tag_directives = [&btd, etd, this](size_t next_node){
+        auto end = btd;
+        while(end < etd)
+        {
+            if(end->next_node_id > next_node)
+                break;
+            ++end;
+        }
+        for( ; btd != end; ++btd)
+        {
+            if(next_node != m_tree->first_child(m_tree->parent(next_node)))
+                this->Writer::_do_write("...\n");
+            this->Writer::_do_write("%TAG ");
+            this->Writer::_do_write(btd->handle);
+            this->Writer::_do_write(' ');
+            this->Writer::_do_write(btd->prefix);
+            this->Writer::_do_write('\n');
+        }
+    };
+    if(m_tree->is_stream(id))
+    {
+        if(m_tree->first_child(id) != NONE)
+            write_tag_directives(m_tree->first_child(id));
+        for(size_t child = m_tree->first_child(id); child != NONE; child = m_tree->next_sibling(child))
+        {
+            dispatch(child);
+            if(m_tree->next_sibling(child) != NONE)
+                write_tag_directives(m_tree->next_sibling(child));
+        }
+    }
+    else if(m_tree->is_container(id))
+    {
+        dispatch(id);
+    }
+    else if(m_tree->is_doc(id))
+    {
+        _RYML_CB_ASSERT(m_tree->callbacks(), !m_tree->is_container(id)); // checked above
+        _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->is_val(id)); // so it must be a val
+        _write_doc(id);
+    }
+    else if(m_tree->is_keyval(id))
+    {
+        _writek(id, 0);
+        this->Writer::_do_write(": ");
+        _writev(id, 0);
+        if(!m_tree->type(id).marked_flow())
+            this->Writer::_do_write('\n');
+    }
+    else if(m_tree->is_val(id))
+    {
+        //this->Writer::_do_write("- ");
+        _writev(id, 0);
+        if(!m_tree->type(id).marked_flow())
+            this->Writer::_do_write('\n');
+    }
+    else if(m_tree->type(id) == NOTYPE)
+    {
+        ;
+    }
+    else
+    {
+        _RYML_CB_ERR(m_tree->callbacks(), "unknown type");
+    }
+}
+
+template<class Writer>
+void Emitter<Writer>::_write_doc(size_t id)
+{
+    RYML_ASSERT(m_tree->is_doc(id));
+    if(!m_tree->is_root(id))
+    {
+        RYML_ASSERT(m_tree->is_stream(m_tree->parent(id)));
+        this->Writer::_do_write("---");
+    }
+    if(!m_tree->has_val(id)) // this is more frequent
+    {
+        if(m_tree->has_val_tag(id))
+        {
+            if(!m_tree->is_root(id))
+                this->Writer::_do_write(' ');
+            _write_tag(m_tree->val_tag(id));
+        }
+        if(m_tree->has_val_anchor(id))
+        {
+            if(!m_tree->is_root(id))
+                this->Writer::_do_write(' ');
+            this->Writer::_do_write('&');
+            this->Writer::_do_write(m_tree->val_anchor(id));
+        }
+    }
+    else // docval
+    {
+        RYML_ASSERT(m_tree->has_val(id));
+        RYML_ASSERT(!m_tree->has_key(id));
+        if(!m_tree->is_root(id))
+            this->Writer::_do_write(' ');
+        _writev(id, 0);
+    }
+    this->Writer::_do_write('\n');
+}
+
+template<class Writer>
+void Emitter<Writer>::_do_visit_flow_sl(size_t node, size_t ilevel)
+{
+    RYML_ASSERT(!m_tree->is_stream(node));
+    RYML_ASSERT(m_tree->is_container(node) || m_tree->is_doc(node));
+    RYML_ASSERT(m_tree->is_root(node) || (m_tree->parent_is_map(node) || m_tree->parent_is_seq(node)));
+
+    if(m_tree->is_doc(node))
+    {
+        _write_doc(node);
+        if(!m_tree->has_children(node))
+            return;
+    }
+    else if(m_tree->is_container(node))
+    {
+        RYML_ASSERT(m_tree->is_map(node) || m_tree->is_seq(node));
+
+        bool spc = false; // write a space
+
+        if(m_tree->has_key(node))
+        {
+            _writek(node, ilevel);
+            this->Writer::_do_write(':');
+            spc = true;
+        }
+
+        if(m_tree->has_val_tag(node))
+        {
+            if(spc)
+                this->Writer::_do_write(' ');
+            _write_tag(m_tree->val_tag(node));
+            spc = true;
+        }
+
+        if(m_tree->has_val_anchor(node))
+        {
+            if(spc)
+                this->Writer::_do_write(' ');
+            this->Writer::_do_write('&');
+            this->Writer::_do_write(m_tree->val_anchor(node));
+            spc = true;
+        }
+
+        if(spc)
+            this->Writer::_do_write(' ');
+
+        if(m_tree->is_map(node))
+        {
+            this->Writer::_do_write('{');
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->is_seq(node));
+            this->Writer::_do_write('[');
+        }
+    } // container
+
+    for(size_t child = m_tree->first_child(node), count = 0; child != NONE; child = m_tree->next_sibling(child))
+    {
+        if(count++)
+            this->Writer::_do_write(',');
+        if(m_tree->is_keyval(child))
+        {
+            _writek(child, ilevel);
+            this->Writer::_do_write(": ");
+            _writev(child, ilevel);
+        }
+        else if(m_tree->is_val(child))
+        {
+            _writev(child, ilevel);
+        }
+        else
+        {
+            // with single-line flow, we can never go back to block
+            _do_visit_flow_sl(child, ilevel + 1);
+        }
+    }
+
+    if(m_tree->is_map(node))
+    {
+        this->Writer::_do_write('}');
+    }
+    else if(m_tree->is_seq(node))
+    {
+        this->Writer::_do_write(']');
+    }
+}
+
+template<class Writer>
+void Emitter<Writer>::_do_visit_flow_ml(size_t id, size_t ilevel, size_t do_indent)
+{
+    C4_UNUSED(id);
+    C4_UNUSED(ilevel);
+    C4_UNUSED(do_indent);
+    RYML_CHECK(false/*not implemented*/);
+}
+
+template<class Writer>
+void Emitter<Writer>::_do_visit_block_container(size_t node, size_t next_level, size_t do_indent)
+{
+    RepC ind = indent_to(do_indent * next_level);
+
+    if(m_tree->is_seq(node))
+    {
+        for(size_t child = m_tree->first_child(node); child != NONE; child = m_tree->next_sibling(child))
+        {
+            _RYML_CB_ASSERT(m_tree->callbacks(), !m_tree->has_key(child));
+            if(m_tree->is_val(child))
+            {
+                this->Writer::_do_write(ind);
+                this->Writer::_do_write("- ");
+                _writev(child, next_level);
+                this->Writer::_do_write('\n');
+            }
+            else
+            {
+                _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->is_container(child));
+                NodeType ty = m_tree->type(child);
+                if(ty.marked_flow_sl())
+                {
+                    this->Writer::_do_write(ind);
+                    this->Writer::_do_write("- ");
+                    _do_visit_flow_sl(child, 0u);
+                    this->Writer::_do_write('\n');
+                }
+                else if(ty.marked_flow_ml())
+                {
+                    this->Writer::_do_write(ind);
+                    this->Writer::_do_write("- ");
+                    _do_visit_flow_ml(child, next_level, do_indent);
+                    this->Writer::_do_write('\n');
+                }
+                else
+                {
+                    _do_visit_block(child, next_level, do_indent);
+                }
+            }
+            do_indent = true;
+            ind = indent_to(do_indent * next_level);
+        }
+    }
+    else // map
+    {
+        _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->is_map(node));
+        for(size_t ich = m_tree->first_child(node); ich != NONE; ich = m_tree->next_sibling(ich))
+        {
+            _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->has_key(ich));
+            if(m_tree->is_keyval(ich))
+            {
+                this->Writer::_do_write(ind);
+                _writek(ich, next_level);
+                this->Writer::_do_write(": ");
+                _writev(ich, next_level);
+                this->Writer::_do_write('\n');
+            }
+            else
+            {
+                _RYML_CB_ASSERT(m_tree->callbacks(), m_tree->is_container(ich));
+                NodeType ty = m_tree->type(ich);
+                if(ty.marked_flow_sl())
+                {
+                    this->Writer::_do_write(ind);
+                    _do_visit_flow_sl(ich, 0u);
+                    this->Writer::_do_write('\n');
+                }
+                else if(ty.marked_flow_ml())
+                {
+                    this->Writer::_do_write(ind);
+                    _do_visit_flow_ml(ich, 0u);
+                    this->Writer::_do_write('\n');
+                }
+                else
+                {
+                    _do_visit_block(ich, next_level, do_indent);
+                }
+            }
+            do_indent = true;
+            ind = indent_to(do_indent * next_level);
+        }
+    }
+}
+
+template<class Writer>
+void Emitter<Writer>::_do_visit_block(size_t node, size_t ilevel, size_t do_indent)
+{
+    RYML_ASSERT(!m_tree->is_stream(node));
+    RYML_ASSERT(m_tree->is_container(node) || m_tree->is_doc(node));
+    RYML_ASSERT(m_tree->is_root(node) || (m_tree->parent_is_map(node) || m_tree->parent_is_seq(node)));
+    RepC ind = indent_to(do_indent * ilevel);
+
+    if(m_tree->is_doc(node))
+    {
+        _write_doc(node);
+        if(!m_tree->has_children(node))
+            return;
+    }
+    else if(m_tree->is_container(node))
+    {
+        RYML_ASSERT(m_tree->is_map(node) || m_tree->is_seq(node));
+
+        bool spc = false; // write a space
+        bool nl = false;  // write a newline
+
+        if(m_tree->has_key(node))
+        {
+            this->Writer::_do_write(ind);
+            _writek(node, ilevel);
+            this->Writer::_do_write(':');
+            spc = true;
+        }
+        else if(!m_tree->is_root(node))
+        {
+            this->Writer::_do_write(ind);
+            this->Writer::_do_write('-');
+            spc = true;
+        }
+
+        if(m_tree->has_val_tag(node))
+        {
+            if(spc)
+                this->Writer::_do_write(' ');
+            _write_tag(m_tree->val_tag(node));
+            spc = true;
+            nl = true;
+        }
+
+        if(m_tree->has_val_anchor(node))
+        {
+            if(spc)
+                this->Writer::_do_write(' ');
+            this->Writer::_do_write('&');
+            this->Writer::_do_write(m_tree->val_anchor(node));
+            spc = true;
+            nl = true;
+        }
+
+        if(m_tree->has_children(node))
+        {
+            if(m_tree->has_key(node))
+                nl = true;
+            else
+                if(!m_tree->is_root(node) && !nl)
+                    spc = true;
+        }
+        else
+        {
+            if(m_tree->is_seq(node))
+                this->Writer::_do_write(" []\n");
+            else if(m_tree->is_map(node))
+                this->Writer::_do_write(" {}\n");
+            return;
+        }
+
+        if(spc && !nl)
+            this->Writer::_do_write(' ');
+
+        do_indent = 0;
+        if(nl)
+        {
+            this->Writer::_do_write('\n');
+            do_indent = 1;
+        }
+    } // container
+
+    size_t next_level = ilevel + 1;
+    if(m_tree->is_root(node) || m_tree->is_doc(node))
+        next_level = ilevel; // do not indent at top level
+
+    _do_visit_block_container(node, next_level, do_indent);
+}
+
+template<class Writer>
+void Emitter<Writer>::_do_visit_json(size_t id)
+{
+    _RYML_CB_CHECK(m_tree->callbacks(), !m_tree->is_stream(id)); // JSON does not have streams
+    if(m_tree->is_keyval(id))
+    {
+        _writek_json(id);
+        this->Writer::_do_write(": ");
+        _writev_json(id);
+    }
+    else if(m_tree->is_val(id))
+    {
+        _writev_json(id);
+    }
+    else if(m_tree->is_container(id))
+    {
+        if(m_tree->has_key(id))
+        {
+            _writek_json(id);
+            this->Writer::_do_write(": ");
+        }
+        if(m_tree->is_seq(id))
+            this->Writer::_do_write('[');
+        else if(m_tree->is_map(id))
+            this->Writer::_do_write('{');
+    }  // container
+
+    for(size_t ich = m_tree->first_child(id); ich != NONE; ich = m_tree->next_sibling(ich))
+    {
+        if(ich != m_tree->first_child(id))
+            this->Writer::_do_write(',');
+        _do_visit_json(ich);
+    }
+
+    if(m_tree->is_seq(id))
+        this->Writer::_do_write(']');
+    else if(m_tree->is_map(id))
+        this->Writer::_do_write('}');
+}
+
+template<class Writer>
+void Emitter<Writer>::_write(NodeScalar const& C4_RESTRICT sc, NodeType flags, size_t ilevel)
+{
+    if( ! sc.tag.empty())
+    {
+        _write_tag(sc.tag);
+        this->Writer::_do_write(' ');
+    }
+    if(flags.has_anchor())
+    {
+        RYML_ASSERT(flags.is_ref() != flags.has_anchor());
+        RYML_ASSERT( ! sc.anchor.empty());
+        this->Writer::_do_write('&');
+        this->Writer::_do_write(sc.anchor);
+        this->Writer::_do_write(' ');
+    }
+    else if(flags.is_ref())
+    {
+        if(sc.anchor != "<<")
+            this->Writer::_do_write('*');
+        this->Writer::_do_write(sc.anchor);
+        return;
+    }
+
+    // ensure the style flags only have one of KEY or VAL
+    _RYML_CB_ASSERT(m_tree->callbacks(), ((flags & (_WIP_KEY_STYLE|_WIP_VAL_STYLE)) == 0) || (((flags&_WIP_KEY_STYLE) == 0) != ((flags&_WIP_VAL_STYLE) == 0)));
+
+    auto style_marks = flags & (_WIP_KEY_STYLE|_WIP_VAL_STYLE);
+    if(style_marks & (_WIP_KEY_LITERAL|_WIP_VAL_LITERAL))
+    {
+        _write_scalar_literal(sc.scalar, ilevel, flags.has_key());
+    }
+    else if(style_marks & (_WIP_KEY_FOLDED|_WIP_VAL_FOLDED))
+    {
+        _write_scalar_folded(sc.scalar, ilevel, flags.has_key());
+    }
+    else if(style_marks & (_WIP_KEY_SQUO|_WIP_VAL_SQUO))
+    {
+        _write_scalar_squo(sc.scalar, ilevel);
+    }
+    else if(style_marks & (_WIP_KEY_DQUO|_WIP_VAL_DQUO))
+    {
+        _write_scalar_dquo(sc.scalar, ilevel);
+    }
+    else if(style_marks & (_WIP_KEY_PLAIN|_WIP_VAL_PLAIN))
+    {
+        _write_scalar_plain(sc.scalar, ilevel);
+    }
+    else if(!style_marks)
+    {
+        size_t first_non_nl = sc.scalar.first_not_of('\n');
+        bool all_newlines = first_non_nl == npos;
+        bool has_leading_ws = (!all_newlines) && sc.scalar.sub(first_non_nl).begins_with_any(" \t");
+        bool do_literal = ((!sc.scalar.empty() && all_newlines) || (has_leading_ws && !sc.scalar.trim(' ').empty()));
+        if(do_literal)
+        {
+            _write_scalar_literal(sc.scalar, ilevel, flags.has_key(), /*explicit_indentation*/has_leading_ws);
+        }
+        else
+        {
+            for(size_t i = 0; i < sc.scalar.len; ++i)
+            {
+                if(sc.scalar.str[i] == '\n')
+                {
+                    _write_scalar_literal(sc.scalar, ilevel, flags.has_key(), /*explicit_indentation*/has_leading_ws);
+                    goto wrote_special;
+                }
+                // todo: check for escaped characters requiring double quotes
+            }
+            _write_scalar(sc.scalar, flags.is_quoted());
+        wrote_special:
+            ;
+        }
+    }
+    else
+    {
+        _RYML_CB_ERR(m_tree->callbacks(), "not implemented");
+    }
+}
+template<class Writer>
+void Emitter<Writer>::_write_json(NodeScalar const& C4_RESTRICT sc, NodeType flags)
+{
+    if(C4_UNLIKELY( ! sc.tag.empty()))
+        _RYML_CB_ERR(m_tree->callbacks(), "JSON does not have tags");
+    if(C4_UNLIKELY(flags.has_anchor()))
+        _RYML_CB_ERR(m_tree->callbacks(), "JSON does not have anchors");
+    _write_scalar_json(sc.scalar, flags.has_key(), flags.is_quoted());
+}
+
+#define _rymlindent_nextline() for(size_t lv = 0; lv < ilevel+1; ++lv) { this->Writer::_do_write(' '); this->Writer::_do_write(' '); }
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar_literal(csubstr s, size_t ilevel, bool explicit_key, bool explicit_indentation)
+{
+    if(explicit_key)
+        this->Writer::_do_write("? ");
+    csubstr trimmed = s.trimr("\n\r");
+    size_t numnewlines_at_end = s.len - trimmed.len - s.sub(trimmed.len).count('\r');
+    //
+    if(!explicit_indentation)
+        this->Writer::_do_write('|');
+    else
+        this->Writer::_do_write("|2");
+    //
+    if(numnewlines_at_end > 1 || (trimmed.len == 0 && s.len > 0)/*only newlines*/)
+        this->Writer::_do_write("+\n");
+    else if(numnewlines_at_end == 1)
+        this->Writer::_do_write('\n');
+    else
+        this->Writer::_do_write("-\n");
+    //
+    if(trimmed.len)
+    {
+        size_t pos = 0; // tracks the last character that was already written
+        for(size_t i = 0; i < trimmed.len; ++i)
+        {
+            if(trimmed[i] != '\n')
+                continue;
+            // write everything up to this point
+            csubstr since_pos = trimmed.range(pos, i+1); // include the newline
+            _rymlindent_nextline()
+            this->Writer::_do_write(since_pos);
+            pos = i+1; // already written
+        }
+        if(pos < trimmed.len)
+        {
+            _rymlindent_nextline()
+            this->Writer::_do_write(trimmed.sub(pos));
+        }
+        if(numnewlines_at_end)
+        {
+            this->Writer::_do_write('\n');
+            --numnewlines_at_end;
+        }
+    }
+    for(size_t i = 0; i < numnewlines_at_end; ++i)
+    {
+        _rymlindent_nextline()
+        if(i+1 < numnewlines_at_end || explicit_key)
+            this->Writer::_do_write('\n');
+    }
+    if(explicit_key && !numnewlines_at_end)
+        this->Writer::_do_write('\n');
+}
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar_folded(csubstr s, size_t ilevel, bool explicit_key)
+{
+    if(explicit_key)
+    {
+        this->Writer::_do_write("? ");
+    }
+    RYML_ASSERT(s.find("\r") == csubstr::npos);
+    csubstr trimmed = s.trimr('\n');
+    size_t numnewlines_at_end = s.len - trimmed.len;
+    if(numnewlines_at_end == 0)
+    {
+        this->Writer::_do_write(">-\n");
+    }
+    else if(numnewlines_at_end == 1)
+    {
+        this->Writer::_do_write(">\n");
+    }
+    else if(numnewlines_at_end > 1)
+    {
+        this->Writer::_do_write(">+\n");
+    }
+    if(trimmed.len)
+    {
+        size_t pos = 0; // tracks the last character that was already written
+        for(size_t i = 0; i < trimmed.len; ++i)
+        {
+            if(trimmed[i] != '\n')
+                continue;
+            // write everything up to this point
+            csubstr since_pos = trimmed.range(pos, i+1); // include the newline
+            pos = i+1; // because of the newline
+            _rymlindent_nextline()
+            this->Writer::_do_write(since_pos);
+            this->Writer::_do_write('\n'); // write the newline twice
+        }
+        if(pos < trimmed.len)
+        {
+            _rymlindent_nextline()
+            this->Writer::_do_write(trimmed.sub(pos));
+        }
+        if(numnewlines_at_end)
+        {
+            this->Writer::_do_write('\n');
+            --numnewlines_at_end;
+        }
+    }
+    for(size_t i = 0; i < numnewlines_at_end; ++i)
+    {
+        _rymlindent_nextline()
+        if(i+1 < numnewlines_at_end || explicit_key)
+            this->Writer::_do_write('\n');
+    }
+    if(explicit_key && !numnewlines_at_end)
+        this->Writer::_do_write('\n');
+}
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar_squo(csubstr s, size_t ilevel)
+{
+    size_t pos = 0; // tracks the last character that was already written
+    this->Writer::_do_write('\'');
+    for(size_t i = 0; i < s.len; ++i)
+    {
+        if(s[i] == '\n')
+        {
+            csubstr sub = s.range(pos, i+1);
+            this->Writer::_do_write(sub);  // write everything up to (including) this char
+            this->Writer::_do_write('\n'); // write the character again
+            if(i + 1 < s.len)
+                _rymlindent_nextline()     // indent the next line
+            pos = i+1;
+        }
+        else if(s[i] == '\'')
+        {
+            csubstr sub = s.range(pos, i+1);
+            this->Writer::_do_write(sub); // write everything up to (including) this char
+            this->Writer::_do_write('\''); // write the character again
+            pos = i+1;
+        }
+    }
+    // write missing characters at the end of the string
+    if(pos < s.len)
+        this->Writer::_do_write(s.sub(pos));
+    this->Writer::_do_write('\'');
+}
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar_dquo(csubstr s, size_t ilevel)
+{
+    size_t pos = 0; // tracks the last character that was already written
+    this->Writer::_do_write('"');
+    for(size_t i = 0; i < s.len; ++i)
+    {
+        const char curr = s.str[i];
+        if(curr == '"' || curr == '\\')
+        {
+            csubstr sub = s.range(pos, i);
+            this->Writer::_do_write(sub);  // write everything up to (excluding) this char
+            this->Writer::_do_write('\\'); // write the escape
+            this->Writer::_do_write(curr); // write the char
+            pos = i+1;
+        }
+        else if(s[i] == '\n')
+        {
+            csubstr sub = s.range(pos, i+1);
+            this->Writer::_do_write(sub);  // write everything up to (including) this newline
+            this->Writer::_do_write('\n'); // write the newline again
+            if(i + 1 < s.len)
+                _rymlindent_nextline()     // indent the next line
+            pos = i+1;
+            if(i+1 < s.len) // escape leading whitespace after the newline
+            {
+                const char next = s.str[i+1];
+                if(next == ' ' || next == '\t')
+                    this->Writer::_do_write('\\');
+            }
+        }
+        else if(curr == ' ' || curr == '\t')
+        {
+            // escape trailing whitespace before a newline
+            size_t next = s.first_not_of(" \t\r", i);
+            if(next != npos && s[next] == '\n')
+            {
+                csubstr sub = s.range(pos, i);
+                this->Writer::_do_write(sub);  // write everything up to (excluding) this char
+                this->Writer::_do_write('\\'); // escape the whitespace
+                pos = i;
+            }
+        }
+        else if(C4_UNLIKELY(curr == '\r'))
+        {
+            csubstr sub = s.range(pos, i);
+            this->Writer::_do_write(sub);  // write everything up to (excluding) this char
+            this->Writer::_do_write("\\r"); // write the escaped char
+            pos = i+1;
+        }
+    }
+    // write missing characters at the end of the string
+    if(pos < s.len)
+    {
+        csubstr sub = s.sub(pos);
+        this->Writer::_do_write(sub);
+    }
+    this->Writer::_do_write('"');
+}
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar_plain(csubstr s, size_t ilevel)
+{
+    size_t pos = 0; // tracks the last character that was already written
+    for(size_t i = 0; i < s.len; ++i)
+    {
+        const char curr = s.str[i];
+        if(curr == '\n')
+        {
+            csubstr sub = s.range(pos, i+1);
+            this->Writer::_do_write(sub);  // write everything up to (including) this newline
+            this->Writer::_do_write('\n'); // write the newline again
+            if(i + 1 < s.len)
+                _rymlindent_nextline()     // indent the next line
+            pos = i+1;
+        }
+    }
+    // write missing characters at the end of the string
+    if(pos < s.len)
+    {
+        csubstr sub = s.sub(pos);
+        this->Writer::_do_write(sub);
+    }
+}
+
+#undef _rymlindent_nextline
+
+template<class Writer>
+void Emitter<Writer>::_write_scalar(csubstr s, bool was_quoted)
+{
+    // this block of code needed to be moved to before the needs_quotes
+    // assignment to work around a g++ optimizer bug where (s.str != nullptr)
+    // was evaluated as true even if s.str was actually a nullptr (!!!)
+    if(s.len == size_t(0))
+    {
+        if(was_quoted || s.str != nullptr)
+            this->Writer::_do_write("''");
+        return;
+    }
+
+    const bool needs_quotes = (
+        was_quoted
+        ||
+        (
+            ( ! s.is_number())
+            &&
+            (
+                // has leading whitespace
+                // looks like reference or anchor
+                // would be treated as a directive
+                // see https://www.yaml.info/learn/quote.html#noplain
+                s.begins_with_any(" \n\t\r*&%@`")
+                ||
+                s.begins_with("<<")
+                ||
+                // has trailing whitespace
+                s.ends_with_any(" \n\t\r")
+                ||
+                // has special chars
+                (s.first_of("#:-?,\n{}[]'\"") != npos)
+            )
+        )
+    );
+
+    if( ! needs_quotes)
+    {
+        this->Writer::_do_write(s);
+    }
+    else
+    {
+        const bool has_dquotes = s.first_of( '"') != npos;
+        const bool has_squotes = s.first_of('\'') != npos;
+        if(!has_squotes && has_dquotes)
+        {
+            this->Writer::_do_write('\'');
+            this->Writer::_do_write(s);
+            this->Writer::_do_write('\'');
+        }
+        else if(has_squotes && !has_dquotes)
+        {
+            RYML_ASSERT(s.count('\n') == 0);
+            this->Writer::_do_write('"');
+            this->Writer::_do_write(s);
+            this->Writer::_do_write('"');
+        }
+        else
+        {
+            _write_scalar_squo(s, /*FIXME FIXME FIXME*/0);
+        }
+    }
+}
+template<class Writer>
+void Emitter<Writer>::_write_scalar_json(csubstr s, bool as_key, bool use_quotes)
+{
+    if((!use_quotes)
+       // json keys require quotes
+       && (!as_key)
+       && (
+           // do not quote special cases
+           (s == "true" || s == "false" || s == "null")
+           || (
+               // do not quote numbers
+               (s.is_number()
+                && (
+                    // quote integral numbers if they have a leading 0
+                    // https://github.com/biojppm/rapidyaml/issues/291
+                    (!(s.len > 1 && s.begins_with('0')))
+                    // do not quote reals with leading 0
+                    // https://github.com/biojppm/rapidyaml/issues/313
+                    || (s.find('.') != csubstr::npos) ))
+               )
+           )
+        )
+    {
+        this->Writer::_do_write(s);
+    }
+    else
+    {
+        size_t pos = 0;
+        this->Writer::_do_write('"');
+        for(size_t i = 0; i < s.len; ++i)
+        {
+            switch(s.str[i])
+            {
+            case '"':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\\"");
+              pos = i + 1;
+              break;
+            case '\n':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\n");
+              pos = i + 1;
+              break;
+            case '\t':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\t");
+              pos = i + 1;
+              break;
+            case '\\':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\\\");
+              pos = i + 1;
+              break;
+            case '\r':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\r");
+              pos = i + 1;
+              break;
+            case '\b':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\b");
+              pos = i + 1;
+              break;
+            case '\f':
+              this->Writer ::_do_write(s.range(pos, i));
+              this->Writer ::_do_write("\\f");
+              pos = i + 1;
+              break;
+            }
+        }
+        if(pos < s.len)
+        {
+            csubstr sub = s.sub(pos);
+            this->Writer::_do_write(sub);
+        }
+        this->Writer::_do_write('"');
+    }
+}
+
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_EMIT_DEF_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/emit.hpp b/thirdparty/ryml/src/c4/yml/emit.hpp
new file mode 100644
index 000000000..c7cdd2a1a
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/emit.hpp
@@ -0,0 +1,490 @@
+#ifndef _C4_YML_EMIT_HPP_
+#define _C4_YML_EMIT_HPP_
+
+#ifndef _C4_YML_WRITER_HPP_
+#include "./writer.hpp"
+#endif
+
+#ifndef _C4_YML_TREE_HPP_
+#include "./tree.hpp"
+#endif
+
+#ifndef _C4_YML_NODE_HPP_
+#include "./node.hpp"
+#endif
+
+
+#define RYML_DEPRECATE_EMIT                                             \
+    RYML_DEPRECATED("use emit_yaml() instead. See https://github.com/biojppm/rapidyaml/issues/120")
+#ifdef emit
+#error "emit is defined, likely from a Qt include. This will cause a compilation error. See https://github.com/biojppm/rapidyaml/issues/120"
+#endif
+#define RYML_DEPRECATE_EMITRS                                           \
+    RYML_DEPRECATED("use emitrs_yaml() instead. See https://github.com/biojppm/rapidyaml/issues/120")
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+namespace c4 {
+namespace yml {
+
+template<class Writer> class Emitter;
+
+template<class OStream>
+using EmitterOStream = Emitter<WriterOStream<OStream>>;
+using EmitterFile = Emitter<WriterFile>;
+using EmitterBuf  = Emitter<WriterBuf>;
+
+typedef enum {
+    EMIT_YAML = 0,
+    EMIT_JSON = 1
+} EmitType_e;
+
+
+/** mark a tree or node to be emitted as json */
+struct as_json
+{
+    Tree const* tree;
+    size_t node;
+    as_json(Tree const& t) : tree(&t), node(t.empty() ? NONE : t.root_id()) {}
+    as_json(Tree const& t, size_t id) : tree(&t), node(id) {}
+    as_json(ConstNodeRef const& n) : tree(n.tree()), node(n.id()) {}
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+template<class Writer>
+class Emitter : public Writer
+{
+public:
+
+    using Writer::Writer;
+
+    /** emit!
+     *
+     * When writing to a buffer, returns a substr of the emitted YAML.
+     * If the given buffer has insufficient space, the returned span will
+     * be null and its size will be the needed space. No writes are done
+     * after the end of the buffer.
+     *
+     * When writing to a file, the returned substr will be null, but its
+     * length will be set to the number of bytes written. */
+    substr emit_as(EmitType_e type, Tree const& t, size_t id, bool error_on_excess);
+    /** emit starting at the root node */
+    substr emit_as(EmitType_e type, Tree const& t, bool error_on_excess=true);
+    /** emit the given node */
+    substr emit_as(EmitType_e type, ConstNodeRef const& n, bool error_on_excess=true);
+
+private:
+
+    Tree const* C4_RESTRICT m_tree;
+
+    void _emit_yaml(size_t id);
+    void _do_visit_flow_sl(size_t id, size_t ilevel=0);
+    void _do_visit_flow_ml(size_t id, size_t ilevel=0, size_t do_indent=1);
+    void _do_visit_block(size_t id, size_t ilevel=0, size_t do_indent=1);
+    void _do_visit_block_container(size_t id, size_t next_level, size_t do_indent);
+    void _do_visit_json(size_t id);
+
+private:
+
+    void _write(NodeScalar const& C4_RESTRICT sc, NodeType flags, size_t level);
+    void _write_json(NodeScalar const& C4_RESTRICT sc, NodeType flags);
+
+    void _write_doc(size_t id);
+    void _write_scalar(csubstr s, bool was_quoted);
+    void _write_scalar_json(csubstr s, bool as_key, bool was_quoted);
+    void _write_scalar_literal(csubstr s, size_t level, bool as_key, bool explicit_indentation=false);
+    void _write_scalar_folded(csubstr s, size_t level, bool as_key);
+    void _write_scalar_squo(csubstr s, size_t level);
+    void _write_scalar_dquo(csubstr s, size_t level);
+    void _write_scalar_plain(csubstr s, size_t level);
+
+    void _write_tag(csubstr tag)
+    {
+        if(!tag.begins_with('!'))
+            this->Writer::_do_write('!');
+        this->Writer::_do_write(tag);
+    }
+
+    enum : type_bits {
+        _keysc =  (KEY|KEYREF|KEYANCH|KEYQUO|_WIP_KEY_STYLE) | ~(VAL|VALREF|VALANCH|VALQUO|_WIP_VAL_STYLE),
+        _valsc = ~(KEY|KEYREF|KEYANCH|KEYQUO|_WIP_KEY_STYLE) |  (VAL|VALREF|VALANCH|VALQUO|_WIP_VAL_STYLE),
+        _keysc_json =  (KEY)  | ~(VAL),
+        _valsc_json = ~(KEY)  |  (VAL),
+    };
+
+    C4_ALWAYS_INLINE void _writek(size_t id, size_t level) { _write(m_tree->keysc(id), m_tree->_p(id)->m_type.type & ~_valsc, level); }
+    C4_ALWAYS_INLINE void _writev(size_t id, size_t level) { _write(m_tree->valsc(id), m_tree->_p(id)->m_type.type & ~_keysc, level); }
+
+    C4_ALWAYS_INLINE void _writek_json(size_t id) { _write_json(m_tree->keysc(id), m_tree->_p(id)->m_type.type & ~(VAL)); }
+    C4_ALWAYS_INLINE void _writev_json(size_t id) { _write_json(m_tree->valsc(id), m_tree->_p(id)->m_type.type & ~(KEY)); }
+
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** emit YAML to the given file. A null file defaults to stdout.
+ * Return the number of bytes written. */
+inline size_t emit_yaml(Tree const& t, size_t id, FILE *f)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_YAML, t, id, /*error_on_excess*/true).len;
+}
+RYML_DEPRECATE_EMIT inline size_t emit(Tree const& t, size_t id, FILE *f)
+{
+    return emit_yaml(t, id, f);
+}
+
+/** emit JSON to the given file. A null file defaults to stdout.
+ * Return the number of bytes written. */
+inline size_t emit_json(Tree const& t, size_t id, FILE *f)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_JSON, t, id, /*error_on_excess*/true).len;
+}
+
+
+/** emit YAML to the given file. A null file defaults to stdout.
+ * Return the number of bytes written.
+ * @overload */
+inline size_t emit_yaml(Tree const& t, FILE *f=nullptr)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_YAML, t, /*error_on_excess*/true).len;
+}
+RYML_DEPRECATE_EMIT inline size_t emit(Tree const& t, FILE *f=nullptr)
+{
+    return emit_yaml(t, f);
+}
+
+/** emit JSON to the given file. A null file defaults to stdout.
+ * Return the number of bytes written.
+ * @overload */
+inline size_t emit_json(Tree const& t, FILE *f=nullptr)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_JSON, t, /*error_on_excess*/true).len;
+}
+
+
+/** emit YAML to the given file. A null file defaults to stdout.
+ * Return the number of bytes written.
+ * @overload */
+inline size_t emit_yaml(ConstNodeRef const& r, FILE *f=nullptr)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_YAML, r, /*error_on_excess*/true).len;
+}
+RYML_DEPRECATE_EMIT inline size_t emit(ConstNodeRef const& r, FILE *f=nullptr)
+{
+    return emit_yaml(r, f);
+}
+
+/** emit JSON to the given file. A null file defaults to stdout.
+ * Return the number of bytes written.
+ * @overload */
+inline size_t emit_json(ConstNodeRef const& r, FILE *f=nullptr)
+{
+    EmitterFile em(f);
+    return em.emit_as(EMIT_JSON, r, /*error_on_excess*/true).len;
+}
+
+
+//-----------------------------------------------------------------------------
+
+/** emit YAML to an STL-like ostream */
+template<class OStream>
+inline OStream& operator<< (OStream& s, Tree const& t)
+{
+    EmitterOStream<OStream> em(s);
+    em.emit_as(EMIT_YAML, t);
+    return s;
+}
+
+/** emit YAML to an STL-like ostream
+ * @overload */
+template<class OStream>
+inline OStream& operator<< (OStream& s, ConstNodeRef const& n)
+{
+    EmitterOStream<OStream> em(s);
+    em.emit_as(EMIT_YAML, n);
+    return s;
+}
+
+/** emit json to an STL-like stream */
+template<class OStream>
+inline OStream& operator<< (OStream& s, as_json const& j)
+{
+    EmitterOStream<OStream> em(s);
+    em.emit_as(EMIT_JSON, *j.tree, j.node, true);
+    return s;
+}
+
+
+//-----------------------------------------------------------------------------
+
+
+/** emit YAML to the given buffer. Return a substr trimmed to the emitted YAML.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload */
+inline substr emit_yaml(Tree const& t, size_t id, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_YAML, t, id, error_on_excess);
+}
+RYML_DEPRECATE_EMIT inline substr emit(Tree const& t, size_t id, substr buf, bool error_on_excess=true)
+{
+    return emit_yaml(t, id, buf, error_on_excess);
+}
+
+/** emit JSON to the given buffer. Return a substr trimmed to the emitted JSON.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload */
+inline substr emit_json(Tree const& t, size_t id, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_JSON, t, id, error_on_excess);
+}
+
+
+/** emit YAML to the given buffer. Return a substr trimmed to the emitted YAML.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload */
+inline substr emit_yaml(Tree const& t, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_YAML, t, error_on_excess);
+}
+RYML_DEPRECATE_EMIT inline substr emit(Tree const& t, substr buf, bool error_on_excess=true)
+{
+    return emit_yaml(t, buf, error_on_excess);
+}
+
+/** emit JSON to the given buffer. Return a substr trimmed to the emitted JSON.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload */
+inline substr emit_json(Tree const& t, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_JSON, t, error_on_excess);
+}
+
+
+/** emit YAML to the given buffer. Return a substr trimmed to the emitted YAML.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload
+ */
+inline substr emit_yaml(ConstNodeRef const& r, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_YAML, r, error_on_excess);
+}
+RYML_DEPRECATE_EMIT inline substr emit(ConstNodeRef const& r, substr buf, bool error_on_excess=true)
+{
+    return emit_yaml(r, buf, error_on_excess);
+}
+
+/** emit JSON to the given buffer. Return a substr trimmed to the emitted JSON.
+ * @param error_on_excess Raise an error if the space in the buffer is insufficient.
+ * @overload
+ */
+inline substr emit_json(ConstNodeRef const& r, substr buf, bool error_on_excess=true)
+{
+    EmitterBuf em(buf);
+    return em.emit_as(EMIT_JSON, r, error_on_excess);
+}
+
+
+//-----------------------------------------------------------------------------
+
+/** emit+resize: emit YAML to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+substr emitrs_yaml(Tree const& t, size_t id, CharOwningContainer * cont)
+{
+    substr buf = to_substr(*cont);
+    substr ret = emit_yaml(t, id, buf, /*error_on_excess*/false);
+    if(ret.str == nullptr && ret.len > 0)
+    {
+        cont->resize(ret.len);
+        buf = to_substr(*cont);
+        ret = emit_yaml(t, id, buf, /*error_on_excess*/true);
+    }
+    return ret;
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS substr emitrs(Tree const& t, size_t id, CharOwningContainer * cont)
+{
+    return emitrs_yaml(t, id, cont);
+}
+
+/** emit+resize: emit JSON to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+substr emitrs_json(Tree const& t, size_t id, CharOwningContainer * cont)
+{
+    substr buf = to_substr(*cont);
+    substr ret = emit_json(t, id, buf, /*error_on_excess*/false);
+    if(ret.str == nullptr && ret.len > 0)
+    {
+        cont->resize(ret.len);
+        buf = to_substr(*cont);
+        ret = emit_json(t, id, buf, /*error_on_excess*/true);
+    }
+    return ret;
+}
+
+
+/** emit+resize: emit YAML to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_yaml(Tree const& t, size_t id)
+{
+    CharOwningContainer c;
+    emitrs_yaml(t, id, &c);
+    return c;
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS CharOwningContainer emitrs(Tree const& t, size_t id)
+{
+    CharOwningContainer c;
+    emitrs_yaml(t, id, &c);
+    return c;
+}
+
+/** emit+resize: emit JSON to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_json(Tree const& t, size_t id)
+{
+    CharOwningContainer c;
+    emitrs_json(t, id, &c);
+    return c;
+}
+
+
+/** emit+resize: YAML to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+substr emitrs_yaml(Tree const& t, CharOwningContainer * cont)
+{
+    if(t.empty())
+        return {};
+    return emitrs_yaml(t, t.root_id(), cont);
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS substr emitrs(Tree const& t, CharOwningContainer * cont)
+{
+    return emitrs_yaml(t, cont);
+}
+
+/** emit+resize: JSON to the given std::string/std::vector-like
+ * container, resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+substr emitrs_json(Tree const& t, CharOwningContainer * cont)
+{
+    if(t.empty())
+        return {};
+    return emitrs_json(t, t.root_id(), cont);
+}
+
+
+/** emit+resize: YAML to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_yaml(Tree const& t)
+{
+    CharOwningContainer c;
+    if(t.empty())
+        return c;
+    emitrs_yaml(t, t.root_id(), &c);
+    return c;
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS CharOwningContainer emitrs(Tree const& t)
+{
+    return emitrs_yaml<CharOwningContainer>(t);
+}
+
+/** emit+resize: JSON to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_json(Tree const& t)
+{
+    CharOwningContainer c;
+    if(t.empty())
+        return c;
+    emitrs_json(t, t.root_id(), &c);
+    return c;
+}
+
+
+/** emit+resize: YAML to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+substr emitrs_yaml(ConstNodeRef const& n, CharOwningContainer * cont)
+{
+    _RYML_CB_CHECK(n.tree()->callbacks(), n.valid());
+    return emitrs_yaml(*n.tree(), n.id(), cont);
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS substr emitrs(ConstNodeRef const& n, CharOwningContainer * cont)
+{
+    return emitrs_yaml(n, cont);
+}
+
+/** emit+resize: JSON to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+substr emitrs_json(ConstNodeRef const& n, CharOwningContainer * cont)
+{
+    _RYML_CB_CHECK(n.tree()->callbacks(), n.valid());
+    return emitrs_json(*n.tree(), n.id(), cont);
+}
+
+
+/** emit+resize: YAML to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted YAML. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_yaml(ConstNodeRef const& n)
+{
+    _RYML_CB_CHECK(n.tree()->callbacks(), n.valid());
+    CharOwningContainer c;
+    emitrs_yaml(*n.tree(), n.id(), &c);
+    return c;
+}
+template<class CharOwningContainer>
+RYML_DEPRECATE_EMITRS CharOwningContainer emitrs(ConstNodeRef const& n)
+{
+    return emitrs_yaml<CharOwningContainer>(n);
+}
+
+/** emit+resize: JSON to the given std::string/std::vector-like container,
+ * resizing it as needed to fit the emitted JSON. */
+template<class CharOwningContainer>
+CharOwningContainer emitrs_json(ConstNodeRef const& n)
+{
+    _RYML_CB_CHECK(n.tree()->callbacks(), n.valid());
+    CharOwningContainer c;
+    emitrs_json(*n.tree(), n.id(), &c);
+    return c;
+}
+
+} // namespace yml
+} // namespace c4
+
+#undef RYML_DEPRECATE_EMIT
+#undef RYML_DEPRECATE_EMITRS
+
+#include "c4/yml/emit.def.hpp"
+
+#endif /* _C4_YML_EMIT_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/export.hpp b/thirdparty/ryml/src/c4/yml/export.hpp
new file mode 100644
index 000000000..6b77f3f8d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/export.hpp
@@ -0,0 +1,18 @@
+#ifndef C4_YML_EXPORT_HPP_
+#define C4_YML_EXPORT_HPP_
+
+#ifdef _WIN32
+    #ifdef RYML_SHARED
+        #ifdef RYML_EXPORTS
+            #define RYML_EXPORT __declspec(dllexport)
+        #else
+            #define RYML_EXPORT __declspec(dllimport)
+        #endif
+    #else
+        #define RYML_EXPORT
+    #endif
+#else
+    #define RYML_EXPORT
+#endif
+
+#endif /* C4_YML_EXPORT_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/node.cpp b/thirdparty/ryml/src/c4/yml/node.cpp
new file mode 100644
index 000000000..50c7a0b60
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/node.cpp
@@ -0,0 +1,30 @@
+#include "c4/yml/node.hpp"
+
+namespace c4 {
+namespace yml {
+
+
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+size_t NodeRef::set_key_serialized(c4::fmt::const_base64_wrapper w)
+{
+    _apply_seed();
+    csubstr encoded = this->to_arena(w);
+    this->set_key(encoded);
+    return encoded.len;
+}
+
+size_t NodeRef::set_val_serialized(c4::fmt::const_base64_wrapper w)
+{
+    _apply_seed();
+    csubstr encoded = this->to_arena(w);
+    this->set_val(encoded);
+    return encoded.len;
+}
+
+} // namespace yml
+} // namespace c4
diff --git a/thirdparty/ryml/src/c4/yml/node.hpp b/thirdparty/ryml/src/c4/yml/node.hpp
new file mode 100644
index 000000000..42ed50442
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/node.hpp
@@ -0,0 +1,1276 @@
+#ifndef _C4_YML_NODE_HPP_
+#define _C4_YML_NODE_HPP_
+
+/** @file node.hpp
+ * @see NodeRef */
+
+#include <cstddef>
+
+#include "c4/yml/tree.hpp"
+#include "c4/base64.hpp"
+
+#ifdef __GNUC__
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wtype-limits"
+#endif
+
+#if defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4251/*needs to have dll-interface to be used by clients of struct*/)
+#   pragma warning(disable: 4296/*expression is always 'boolean_value'*/)
+#endif
+
+namespace c4 {
+namespace yml {
+
+template<class K> struct Key { K & k; };
+template<> struct Key<fmt::const_base64_wrapper> { fmt::const_base64_wrapper wrapper; };
+template<> struct Key<fmt::base64_wrapper> { fmt::base64_wrapper wrapper; };
+
+template<class K> C4_ALWAYS_INLINE Key<K> key(K & k) { return Key<K>{k}; }
+C4_ALWAYS_INLINE Key<fmt::const_base64_wrapper> key(fmt::const_base64_wrapper w) { return {w}; }
+C4_ALWAYS_INLINE Key<fmt::base64_wrapper> key(fmt::base64_wrapper w) { return {w}; }
+
+template<class T> void write(NodeRef *n, T const& v);
+
+template<class T>
+typename std::enable_if< ! std::is_floating_point<T>::value, bool>::type
+read(NodeRef const& n, T *v);
+
+template<class T>
+typename std::enable_if<   std::is_floating_point<T>::value, bool>::type
+read(NodeRef const& n, T *v);
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+// forward decls
+class NodeRef;
+class ConstNodeRef;
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+namespace detail {
+
+template<class NodeRefType>
+struct child_iterator
+{
+    using value_type = NodeRefType;
+    using tree_type = typename NodeRefType::tree_type;
+
+    tree_type * C4_RESTRICT m_tree;
+    size_t m_child_id;
+
+    child_iterator(tree_type * t, size_t id) : m_tree(t), m_child_id(id) {}
+
+    child_iterator& operator++ () { RYML_ASSERT(m_child_id != NONE); m_child_id = m_tree->next_sibling(m_child_id); return *this; }
+    child_iterator& operator-- () { RYML_ASSERT(m_child_id != NONE); m_child_id = m_tree->prev_sibling(m_child_id); return *this; }
+
+    NodeRefType operator*  () const { return NodeRefType(m_tree, m_child_id); }
+    NodeRefType operator-> () const { return NodeRefType(m_tree, m_child_id); }
+
+    bool operator!= (child_iterator that) const { RYML_ASSERT(m_tree == that.m_tree); return m_child_id != that.m_child_id; }
+    bool operator== (child_iterator that) const { RYML_ASSERT(m_tree == that.m_tree); return m_child_id == that.m_child_id; }
+};
+
+template<class NodeRefType>
+struct children_view_
+{
+    using n_iterator = child_iterator<NodeRefType>;
+
+    n_iterator b, e;
+
+    inline children_view_(n_iterator const& C4_RESTRICT b_,
+                          n_iterator const& C4_RESTRICT e_) : b(b_), e(e_) {}
+
+    inline n_iterator begin() const { return b; }
+    inline n_iterator end  () const { return e; }
+};
+
+template<class NodeRefType, class Visitor>
+bool _visit(NodeRefType &node, Visitor fn, size_t indentation_level, bool skip_root=false)
+{
+    size_t increment = 0;
+    if( ! (node.is_root() && skip_root))
+    {
+        if(fn(node, indentation_level))
+            return true;
+        ++increment;
+    }
+    if(node.has_children())
+    {
+        for(auto ch : node.children())
+        {
+            if(_visit(ch, fn, indentation_level + increment, false)) // no need to forward skip_root as it won't be root
+            {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+template<class NodeRefType, class Visitor>
+bool _visit_stacked(NodeRefType &node, Visitor fn, size_t indentation_level, bool skip_root=false)
+{
+    size_t increment = 0;
+    if( ! (node.is_root() && skip_root))
+    {
+        if(fn(node, indentation_level))
+        {
+            return true;
+        }
+        ++increment;
+    }
+    if(node.has_children())
+    {
+        fn.push(node, indentation_level);
+        for(auto ch : node.children())
+        {
+            if(_visit_stacked(ch, fn, indentation_level + increment, false)) // no need to forward skip_root as it won't be root
+            {
+                fn.pop(node, indentation_level);
+                return true;
+            }
+        }
+        fn.pop(node, indentation_level);
+    }
+    return false;
+}
+
+
+//-----------------------------------------------------------------------------
+
+/** a CRTP base for read-only node methods */
+template<class Impl, class ConstImpl>
+struct RoNodeMethods
+{
+    C4_SUPPRESS_WARNING_GCC_CLANG_WITH_PUSH("-Wcast-align")
+    // helper CRTP macros, undefined at the end
+    #define tree_ ((ConstImpl const* C4_RESTRICT)this)->m_tree
+    #define id_ ((ConstImpl const* C4_RESTRICT)this)->m_id
+    #define tree__ ((Impl const* C4_RESTRICT)this)->m_tree
+    #define id__ ((Impl const* C4_RESTRICT)this)->m_id
+    // require valid
+    #define _C4RV()                                       \
+        RYML_ASSERT(tree_ != nullptr);                    \
+        _RYML_CB_ASSERT(tree_->m_callbacks, id_ != NONE)
+    #define _C4_IF_MUTABLE(ty) typename std::enable_if<!std::is_same<U, ConstImpl>::value, ty>::type
+
+public:
+
+    /** @name node property getters */
+    /** @{ */
+
+    /** returns the data or null when the id is NONE */
+    C4_ALWAYS_INLINE C4_PURE NodeData const* get() const noexcept { RYML_ASSERT(tree_ != nullptr); return tree_->get(id_); }
+    /** returns the data or null when the id is NONE */
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto get() noexcept -> _C4_IF_MUTABLE(NodeData*) { RYML_ASSERT(tree_ != nullptr); return tree__->get(id__); }
+
+    C4_ALWAYS_INLINE C4_PURE NodeType    type() const noexcept { _C4RV(); return tree_->type(id_); }
+    C4_ALWAYS_INLINE C4_PURE const char* type_str() const noexcept { return tree_->type_str(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE csubstr key()        const noexcept { _C4RV(); return tree_->key(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr key_tag()    const noexcept { _C4RV(); return tree_->key_tag(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr key_ref()    const noexcept { _C4RV(); return tree_->key_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr key_anchor() const noexcept { _C4RV(); return tree_->key_anchor(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE csubstr val()        const noexcept { _C4RV(); return tree_->val(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr val_tag()    const noexcept { _C4RV(); return tree_->val_tag(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr val_ref()    const noexcept { _C4RV(); return tree_->val_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE csubstr val_anchor() const noexcept { _C4RV(); return tree_->val_anchor(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE NodeScalar const& keysc() const noexcept { _C4RV(); return tree_->keysc(id_); }
+    C4_ALWAYS_INLINE C4_PURE NodeScalar const& valsc() const noexcept { _C4RV(); return tree_->valsc(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE bool key_is_null() const noexcept { _C4RV(); return tree_->key_is_null(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool val_is_null() const noexcept { _C4RV(); return tree_->val_is_null(id_); }
+
+    /** @} */
+
+public:
+
+    /** @name node property predicates */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE bool empty()            const noexcept { _C4RV(); return tree_->empty(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_stream()        const noexcept { _C4RV(); return tree_->is_stream(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_doc()           const noexcept { _C4RV(); return tree_->is_doc(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_container()     const noexcept { _C4RV(); return tree_->is_container(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_map()           const noexcept { _C4RV(); return tree_->is_map(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_seq()           const noexcept { _C4RV(); return tree_->is_seq(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_val()          const noexcept { _C4RV(); return tree_->has_val(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_key()          const noexcept { _C4RV(); return tree_->has_key(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_val()           const noexcept { _C4RV(); return tree_->is_val(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_keyval()        const noexcept { _C4RV(); return tree_->is_keyval(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_key_tag()      const noexcept { _C4RV(); return tree_->has_key_tag(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_val_tag()      const noexcept { _C4RV(); return tree_->has_val_tag(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_key_anchor()   const noexcept { _C4RV(); return tree_->has_key_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_key_anchor()    const noexcept { _C4RV(); return tree_->is_key_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_val_anchor()   const noexcept { _C4RV(); return tree_->has_val_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_val_anchor()    const noexcept { _C4RV(); return tree_->is_val_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_anchor()       const noexcept { _C4RV(); return tree_->has_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_anchor()        const noexcept { _C4RV(); return tree_->is_anchor(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_key_ref()       const noexcept { _C4RV(); return tree_->is_key_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_val_ref()       const noexcept { _C4RV(); return tree_->is_val_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_ref()           const noexcept { _C4RV(); return tree_->is_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_anchor_or_ref() const noexcept { _C4RV(); return tree_->is_anchor_or_ref(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_key_quoted()    const noexcept { _C4RV(); return tree_->is_key_quoted(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_val_quoted()    const noexcept { _C4RV(); return tree_->is_val_quoted(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool is_quoted()        const noexcept { _C4RV(); return tree_->is_quoted(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool parent_is_seq()    const noexcept { _C4RV(); return tree_->parent_is_seq(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool parent_is_map()    const noexcept { _C4RV(); return tree_->parent_is_map(id_); }
+
+    /** @} */
+
+public:
+
+    /** @name hierarchy predicates */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE bool is_root()    const noexcept { _C4RV(); return tree_->is_root(id_); }
+    C4_ALWAYS_INLINE C4_PURE bool has_parent() const noexcept { _C4RV(); return tree_->has_parent(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE bool has_child(ConstImpl const& ch) const noexcept { _C4RV(); return tree_->has_child(id_, ch.m_id); }
+    C4_ALWAYS_INLINE C4_PURE bool has_child(csubstr name) const noexcept { _C4RV(); return tree_->has_child(id_, name); }
+    C4_ALWAYS_INLINE C4_PURE bool has_children() const noexcept { _C4RV(); return tree_->has_children(id_); }
+
+    C4_ALWAYS_INLINE C4_PURE bool has_sibling(ConstImpl const& n) const noexcept { _C4RV(); return tree_->has_sibling(id_, n.m_id); }
+    C4_ALWAYS_INLINE C4_PURE bool has_sibling(csubstr name) const noexcept { _C4RV(); return tree_->has_sibling(id_, name); }
+    /** counts with this */
+    C4_ALWAYS_INLINE C4_PURE bool has_siblings() const noexcept { _C4RV(); return tree_->has_siblings(id_); }
+    /** does not count with this */
+    C4_ALWAYS_INLINE C4_PURE bool has_other_siblings() const noexcept { _C4RV(); return tree_->has_other_siblings(id_); }
+
+    /** @} */
+
+public:
+
+    /** @name hierarchy getters */
+    /** @{ */
+
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto doc(size_t num) noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->doc(num)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl doc(size_t num) const noexcept { _C4RV(); return {tree_, tree_->doc(num)}; }
+
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto parent() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->parent(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl parent() const noexcept { _C4RV(); return {tree_, tree_->parent(id_)}; }
+
+
+    /** O(#num_children) */
+    C4_ALWAYS_INLINE C4_PURE size_t child_pos(ConstImpl const& n) const noexcept { _C4RV(); return tree_->child_pos(id_, n.m_id); }
+    C4_ALWAYS_INLINE C4_PURE size_t num_children() const noexcept { _C4RV(); return tree_->num_children(id_); }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto first_child() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->first_child(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl first_child() const noexcept { _C4RV(); return {tree_, tree_->first_child(id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto last_child() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->last_child(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl last_child () const noexcept { _C4RV(); return {tree_, tree_->last_child (id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto child(size_t pos) noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->child(id__, pos)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl child(size_t pos) const noexcept { _C4RV(); return {tree_, tree_->child(id_, pos)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto find_child(csubstr name)  noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->find_child(id__, name)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl find_child(csubstr name) const noexcept { _C4RV(); return {tree_, tree_->find_child(id_, name)}; }
+
+
+    /** O(#num_siblings) */
+    C4_ALWAYS_INLINE C4_PURE size_t num_siblings() const noexcept { _C4RV(); return tree_->num_siblings(id_); }
+    C4_ALWAYS_INLINE C4_PURE size_t num_other_siblings() const noexcept { _C4RV(); return tree_->num_other_siblings(id_); }
+    C4_ALWAYS_INLINE C4_PURE size_t sibling_pos(ConstImpl const& n) const noexcept { _C4RV(); return tree_->child_pos(tree_->parent(id_), n.m_id); }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto prev_sibling() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->prev_sibling(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl prev_sibling() const noexcept { _C4RV(); return {tree_, tree_->prev_sibling(id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto next_sibling() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->next_sibling(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl next_sibling() const noexcept { _C4RV(); return {tree_, tree_->next_sibling(id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto first_sibling() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->first_sibling(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl first_sibling() const noexcept { _C4RV(); return {tree_, tree_->first_sibling(id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto last_sibling() noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->last_sibling(id__)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl last_sibling () const noexcept { _C4RV(); return {tree_, tree_->last_sibling(id_)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto sibling(size_t pos) noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->sibling(id__, pos)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl sibling(size_t pos) const noexcept { _C4RV(); return {tree_, tree_->sibling(id_, pos)}; }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto find_sibling(csubstr name) noexcept -> _C4_IF_MUTABLE(Impl) { _C4RV(); return {tree__, tree__->find_sibling(id__, name)}; }
+    C4_ALWAYS_INLINE C4_PURE ConstImpl find_sibling(csubstr name) const noexcept { _C4RV(); return {tree_, tree_->find_sibling(id_, name)}; }
+
+
+    /** O(num_children) */
+    C4_ALWAYS_INLINE C4_PURE ConstImpl operator[] (csubstr k) const noexcept
+    {
+        _C4RV();
+        size_t ch = tree_->find_child(id_, k);
+        _RYML_CB_ASSERT(tree_->m_callbacks, ch != NONE);
+        return {tree_, ch};
+    }
+    /** Find child by key. O(num_children). returns a seed node if no such child is found.  */
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto operator[] (csubstr k) noexcept -> _C4_IF_MUTABLE(Impl)
+    {
+        _C4RV();
+        size_t ch = tree__->find_child(id__, k);
+        return ch != NONE ? Impl(tree__, ch) : NodeRef(tree__, id__, k);
+    }
+
+    /** O(num_children) */
+    C4_ALWAYS_INLINE C4_PURE ConstImpl operator[] (size_t pos) const noexcept
+    {
+        _C4RV();
+        size_t ch = tree_->child(id_, pos);
+        _RYML_CB_ASSERT(tree_->m_callbacks, ch != NONE);
+        return {tree_, ch};
+    }
+
+    /** Find child by position. O(pos). returns a seed node if no such child is found.  */
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto operator[] (size_t pos) noexcept -> _C4_IF_MUTABLE(Impl)
+    {
+        _C4RV();
+        size_t ch = tree__->child(id__, pos);
+        return ch != NONE ? Impl(tree__, ch) : NodeRef(tree__, id__, pos);
+    }
+
+    /** @} */
+
+public:
+
+    /** deserialization */
+    /** @{ */
+
+    template<class T>
+    ConstImpl const& operator>> (T &v) const
+    {
+        _C4RV();
+        if( ! read((ConstImpl const&)*this, &v))
+            _RYML_CB_ERR(tree_->m_callbacks, "could not deserialize value");
+        return *((ConstImpl const*)this);
+    }
+
+    /** deserialize the node's key to the given variable */
+    template<class T>
+    ConstImpl const& operator>> (Key<T> v) const
+    {
+        _C4RV();
+        if( ! from_chars(key(), &v.k))
+            _RYML_CB_ERR(tree_->m_callbacks, "could not deserialize key");
+        return *((ConstImpl const*)this);
+    }
+
+    /** deserialize the node's key as base64 */
+    ConstImpl const& operator>> (Key<fmt::base64_wrapper> w) const
+    {
+        deserialize_key(w.wrapper);
+        return *((ConstImpl const*)this);
+    }
+
+    /** deserialize the node's val as base64 */
+    ConstImpl const& operator>> (fmt::base64_wrapper w) const
+    {
+        deserialize_val(w);
+        return *((ConstImpl const*)this);
+    }
+
+    /** decode the base64-encoded key and assign the
+     * decoded blob to the given buffer/
+     * @return the size of base64-decoded blob */
+    size_t deserialize_key(fmt::base64_wrapper v) const
+    {
+        _C4RV();
+        return from_chars(key(), &v);
+    }
+    /** decode the base64-encoded key and assign the
+     * decoded blob to the given buffer/
+     * @return the size of base64-decoded blob */
+    size_t deserialize_val(fmt::base64_wrapper v) const
+    {
+        _C4RV();
+        return from_chars(val(), &v);
+    };
+
+    template<class T>
+    bool get_if(csubstr name, T *var) const
+    {
+        auto ch = find_child(name);
+        if(!ch.valid())
+            return false;
+        ch >> *var;
+        return true;
+    }
+
+    template<class T>
+    bool get_if(csubstr name, T *var, T const& fallback) const
+    {
+        auto ch = find_child(name);
+        if(ch.valid())
+        {
+            ch >> *var;
+            return true;
+        }
+        else
+        {
+            *var = fallback;
+            return false;
+        }
+    }
+
+    /** @} */
+
+public:
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic push
+    #   pragma clang diagnostic ignored "-Wnull-dereference"
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic push
+    #   if __GNUC__ >= 6
+    #       pragma GCC diagnostic ignored "-Wnull-dereference"
+    #   endif
+    #endif
+
+    /** @name iteration */
+    /** @{ */
+
+    using iterator = detail::child_iterator<Impl>;
+    using const_iterator = detail::child_iterator<ConstImpl>;
+    using children_view = detail::children_view_<Impl>;
+    using const_children_view = detail::children_view_<ConstImpl>;
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto begin() noexcept -> _C4_IF_MUTABLE(iterator) { _C4RV(); return iterator(tree__, tree__->first_child(id__)); }
+    C4_ALWAYS_INLINE C4_PURE const_iterator begin() const noexcept { _C4RV(); return const_iterator(tree_, tree_->first_child(id_)); }
+    C4_ALWAYS_INLINE C4_PURE const_iterator cbegin() const noexcept { _C4RV(); return const_iterator(tree_, tree_->first_child(id_)); }
+
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto end() noexcept -> _C4_IF_MUTABLE(iterator) { _C4RV(); return iterator(tree__, NONE); }
+    C4_ALWAYS_INLINE C4_PURE const_iterator end() const noexcept { _C4RV(); return const_iterator(tree_, NONE); }
+    C4_ALWAYS_INLINE C4_PURE const_iterator cend() const noexcept { _C4RV(); return const_iterator(tree_, tree_->first_child(id_)); }
+
+    /** get an iterable view over children */
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto children() noexcept -> _C4_IF_MUTABLE(children_view) { _C4RV(); return children_view(begin(), end()); }
+    /** get an iterable view over children */
+    C4_ALWAYS_INLINE C4_PURE const_children_view children() const noexcept { _C4RV(); return const_children_view(begin(), end()); }
+    /** get an iterable view over children */
+    C4_ALWAYS_INLINE C4_PURE const_children_view cchildren() const noexcept { _C4RV(); return const_children_view(begin(), end()); }
+
+    /** get an iterable view over all siblings (including the calling node) */
+    template<class U=Impl>
+    C4_ALWAYS_INLINE C4_PURE auto siblings() noexcept -> _C4_IF_MUTABLE(children_view)
+    {
+        _C4RV();
+        NodeData const *nd = tree__->get(id__);
+        return (nd->m_parent != NONE) ? // does it have a parent?
+            children_view(iterator(tree__, tree_->get(nd->m_parent)->m_first_child), iterator(tree__, NONE))
+            :
+            children_view(end(), end());
+    }
+    /** get an iterable view over all siblings (including the calling node) */
+    C4_ALWAYS_INLINE C4_PURE const_children_view siblings() const noexcept
+    {
+        _C4RV();
+        NodeData const *nd = tree_->get(id_);
+        return (nd->m_parent != NONE) ? // does it have a parent?
+            const_children_view(const_iterator(tree_, tree_->get(nd->m_parent)->m_first_child), const_iterator(tree_, NONE))
+            :
+            const_children_view(end(), end());
+    }
+    /** get an iterable view over all siblings (including the calling node) */
+    C4_ALWAYS_INLINE C4_PURE const_children_view csiblings() const noexcept { return siblings(); }
+
+    /** visit every child node calling fn(node) */
+    template<class Visitor>
+    C4_ALWAYS_INLINE C4_PURE bool visit(Visitor fn, size_t indentation_level=0, bool skip_root=true) const noexcept
+    {
+        return detail::_visit(*(ConstImpl*)this, fn, indentation_level, skip_root);
+    }
+    /** visit every child node calling fn(node) */
+    template<class Visitor, class U=Impl>
+    auto visit(Visitor fn, size_t indentation_level=0, bool skip_root=true) noexcept
+        -> _C4_IF_MUTABLE(bool)
+    {
+        return detail::_visit(*(Impl*)this, fn, indentation_level, skip_root);
+    }
+
+    /** visit every child node calling fn(node, level) */
+    template<class Visitor>
+    C4_ALWAYS_INLINE C4_PURE bool visit_stacked(Visitor fn, size_t indentation_level=0, bool skip_root=true) const noexcept
+    {
+        return detail::_visit_stacked(*(ConstImpl*)this, fn, indentation_level, skip_root);
+    }
+    /** visit every child node calling fn(node, level) */
+    template<class Visitor, class U=Impl>
+    auto visit_stacked(Visitor fn, size_t indentation_level=0, bool skip_root=true) noexcept
+        -> _C4_IF_MUTABLE(bool)
+    {
+        return detail::_visit_stacked(*(Impl*)this, fn, indentation_level, skip_root);
+    }
+
+    /** @} */
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic pop
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic pop
+    #endif
+
+    #undef _C4_IF_MUTABLE
+    #undef _C4RV
+    #undef tree_
+    #undef tree__
+    #undef id_
+    #undef id__
+
+    C4_SUPPRESS_WARNING_GCC_CLANG_POP
+};
+
+} // namespace detail
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+class RYML_EXPORT ConstNodeRef : public detail::RoNodeMethods<ConstNodeRef, ConstNodeRef>
+{
+public:
+
+    using tree_type = Tree const;
+
+public:
+
+    Tree const* C4_RESTRICT m_tree;
+    size_t m_id;
+
+    friend NodeRef;
+    friend struct detail::RoNodeMethods<ConstNodeRef, ConstNodeRef>;
+
+public:
+
+    /** @name construction */
+    /** @{ */
+
+    ConstNodeRef() : m_tree(nullptr), m_id(NONE) {}
+    ConstNodeRef(Tree const &t) : m_tree(&t), m_id(t .root_id()) {}
+    ConstNodeRef(Tree const *t) : m_tree(t ), m_id(t->root_id()) {}
+    ConstNodeRef(Tree const *t, size_t id) : m_tree(t), m_id(id) {}
+    ConstNodeRef(std::nullptr_t) : m_tree(nullptr), m_id(NONE) {}
+
+    ConstNodeRef(ConstNodeRef const&) = default;
+    ConstNodeRef(ConstNodeRef     &&) = default;
+
+    ConstNodeRef(NodeRef const&);
+    ConstNodeRef(NodeRef     &&);
+
+    /** @} */
+
+public:
+
+    /** @name assignment */
+    /** @{ */
+
+    ConstNodeRef& operator= (std::nullptr_t) { m_tree = nullptr; m_id = NONE; return *this; }
+
+    ConstNodeRef& operator= (ConstNodeRef const&) = default;
+    ConstNodeRef& operator= (ConstNodeRef     &&) = default;
+
+    ConstNodeRef& operator= (NodeRef const&);
+    ConstNodeRef& operator= (NodeRef     &&);
+
+
+    /** @} */
+
+public:
+
+    /** @name state queries */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE bool valid() const noexcept { return m_tree != nullptr && m_id != NONE; }
+
+    /** @} */
+
+public:
+
+    /** @name member getters */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE Tree const* tree() const noexcept { return m_tree; }
+    C4_ALWAYS_INLINE C4_PURE size_t id() const noexcept { return m_id; }
+
+    /** @} */
+
+public:
+
+    /** @name comparisons */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE bool operator== (ConstNodeRef const& that) const noexcept { RYML_ASSERT(that.m_tree == m_tree); return m_id == that.m_id; }
+    C4_ALWAYS_INLINE C4_PURE bool operator!= (ConstNodeRef const& that) const noexcept { RYML_ASSERT(that.m_tree == m_tree); return ! this->operator==(that); }
+
+    C4_ALWAYS_INLINE C4_PURE bool operator== (std::nullptr_t) const noexcept { return m_tree == nullptr || m_id == NONE; }
+    C4_ALWAYS_INLINE C4_PURE bool operator!= (std::nullptr_t) const noexcept { return ! this->operator== (nullptr); }
+
+    C4_ALWAYS_INLINE C4_PURE bool operator== (csubstr val) const noexcept { RYML_ASSERT(has_val()); return m_tree->val(m_id) == val; }
+    C4_ALWAYS_INLINE C4_PURE bool operator!= (csubstr val) const noexcept { RYML_ASSERT(has_val()); return m_tree->val(m_id) != val; }
+
+    /** @} */
+
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** a reference to a node in an existing yaml tree, offering a more
+ * convenient API than the index-based API used in the tree. */
+class RYML_EXPORT NodeRef : public detail::RoNodeMethods<NodeRef, ConstNodeRef>
+{
+public:
+
+    using tree_type = Tree;
+    using base_type = detail::RoNodeMethods<NodeRef, ConstNodeRef>;
+
+private:
+
+    Tree *C4_RESTRICT m_tree;
+    size_t m_id;
+
+    /** This member is used to enable lazy operator[] writing. When a child
+     * with a key or index is not found, m_id is set to the id of the parent
+     * and the asked-for key or index are stored in this member until a write
+     * does happen. Then it is given as key or index for creating the child.
+     * When a key is used, the csubstr stores it (so the csubstr's string is
+     * non-null and the csubstr's size is different from NONE). When an index is
+     * used instead, the csubstr's string is set to null, and only the csubstr's
+     * size is set to a value different from NONE. Otherwise, when operator[]
+     * does find the child then this member is empty: the string is null and
+     * the size is NONE. */
+    csubstr m_seed;
+
+    friend ConstNodeRef;
+    friend struct detail::RoNodeMethods<NodeRef, ConstNodeRef>;
+
+    // require valid: a helper macro, undefined at the end
+    #define _C4RV()                                                         \
+        RYML_ASSERT(m_tree != nullptr);                                     \
+        _RYML_CB_ASSERT(m_tree->m_callbacks, m_id != NONE && !is_seed())
+
+public:
+
+    /** @name construction */
+    /** @{ */
+
+    NodeRef() : m_tree(nullptr), m_id(NONE), m_seed() { _clear_seed(); }
+    NodeRef(Tree &t) : m_tree(&t), m_id(t .root_id()), m_seed() { _clear_seed(); }
+    NodeRef(Tree *t) : m_tree(t ), m_id(t->root_id()), m_seed() { _clear_seed(); }
+    NodeRef(Tree *t, size_t id) : m_tree(t), m_id(id), m_seed() { _clear_seed(); }
+    NodeRef(Tree *t, size_t id, size_t seed_pos) : m_tree(t), m_id(id), m_seed() { m_seed.str = nullptr; m_seed.len = seed_pos; }
+    NodeRef(Tree *t, size_t id, csubstr  seed_key) : m_tree(t), m_id(id), m_seed(seed_key) {}
+    NodeRef(std::nullptr_t) : m_tree(nullptr), m_id(NONE), m_seed() {}
+
+    /** @} */
+
+public:
+
+    /** @name assignment */
+    /** @{ */
+
+    NodeRef(NodeRef const&) = default;
+    NodeRef(NodeRef     &&) = default;
+
+    NodeRef& operator= (NodeRef const&) = default;
+    NodeRef& operator= (NodeRef     &&) = default;
+
+    /** @} */
+
+public:
+
+    /** @name state queries */
+    /** @{ */
+
+    inline bool valid() const { return m_tree != nullptr && m_id != NONE; }
+    inline bool is_seed() const { return m_seed.str != nullptr || m_seed.len != NONE; }
+
+    inline void _clear_seed() { /*do this manually or an assert is triggered*/ m_seed.str = nullptr; m_seed.len = NONE; }
+
+    /** @} */
+
+public:
+
+    /** @name comparisons */
+    /** @{ */
+
+    inline bool operator== (NodeRef const& that) const { _C4RV(); RYML_ASSERT(that.valid() && !that.is_seed()); RYML_ASSERT(that.m_tree == m_tree); return m_id == that.m_id; }
+    inline bool operator!= (NodeRef const& that) const { return ! this->operator==(that); }
+
+    inline bool operator== (ConstNodeRef const& that) const { _C4RV(); RYML_ASSERT(that.valid()); RYML_ASSERT(that.m_tree == m_tree); return m_id == that.m_id; }
+    inline bool operator!= (ConstNodeRef const& that) const { return ! this->operator==(that); }
+
+    inline bool operator== (std::nullptr_t) const { return m_tree == nullptr || m_id == NONE || is_seed(); }
+    inline bool operator!= (std::nullptr_t) const { return m_tree != nullptr && m_id != NONE && !is_seed(); }
+
+    inline bool operator== (csubstr val) const { _C4RV(); RYML_ASSERT(has_val()); return m_tree->val(m_id) == val; }
+    inline bool operator!= (csubstr val) const { _C4RV(); RYML_ASSERT(has_val()); return m_tree->val(m_id) != val; }
+
+    //inline operator bool () const { return m_tree == nullptr || m_id == NONE || is_seed(); }
+
+    /** @} */
+
+public:
+
+    /** @name node property getters */
+    /** @{ */
+
+    C4_ALWAYS_INLINE C4_PURE Tree * tree() noexcept { return m_tree; }
+    C4_ALWAYS_INLINE C4_PURE Tree const* tree() const noexcept { return m_tree; }
+
+    C4_ALWAYS_INLINE C4_PURE size_t id() const noexcept { return m_id; }
+
+    /** @} */
+
+public:
+
+    /** @name node modifiers */
+    /** @{ */
+
+    void change_type(NodeType t) { _C4RV(); m_tree->change_type(m_id, t); }
+
+    void set_type(NodeType t) { _C4RV(); m_tree->_set_flags(m_id, t); }
+    void set_key(csubstr key) { _C4RV(); m_tree->_set_key(m_id, key); }
+    void set_val(csubstr val) { _C4RV(); m_tree->_set_val(m_id, val); }
+    void set_key_tag(csubstr key_tag) { _C4RV(); m_tree->set_key_tag(m_id, key_tag); }
+    void set_val_tag(csubstr val_tag) { _C4RV(); m_tree->set_val_tag(m_id, val_tag); }
+    void set_key_anchor(csubstr key_anchor) { _C4RV(); m_tree->set_key_anchor(m_id, key_anchor); }
+    void set_val_anchor(csubstr val_anchor) { _C4RV(); m_tree->set_val_anchor(m_id, val_anchor); }
+    void set_key_ref(csubstr key_ref) { _C4RV(); m_tree->set_key_ref(m_id, key_ref); }
+    void set_val_ref(csubstr val_ref) { _C4RV(); m_tree->set_val_ref(m_id, val_ref); }
+
+    template<class T>
+    size_t set_key_serialized(T const& C4_RESTRICT k)
+    {
+        _C4RV();
+        csubstr s = m_tree->to_arena(k);
+        m_tree->_set_key(m_id, s);
+        return s.len;
+    }
+    template<class T>
+    size_t set_val_serialized(T const& C4_RESTRICT v)
+    {
+        _C4RV();
+        csubstr s = m_tree->to_arena(v);
+        m_tree->_set_val(m_id, s);
+        return s.len;
+    }
+    size_t set_val_serialized(std::nullptr_t)
+    {
+        _C4RV();
+        m_tree->_set_val(m_id, csubstr{});
+        return 0;
+    }
+
+    /** encode a blob as base64, then assign the result to the node's key
+     * @return the size of base64-encoded blob */
+    size_t set_key_serialized(fmt::const_base64_wrapper w);
+    /** encode a blob as base64, then assign the result to the node's val
+     * @return the size of base64-encoded blob */
+    size_t set_val_serialized(fmt::const_base64_wrapper w);
+
+public:
+
+    inline void clear()
+    {
+        if(is_seed())
+            return;
+        m_tree->remove_children(m_id);
+        m_tree->_clear(m_id);
+    }
+
+    inline void clear_key()
+    {
+        if(is_seed())
+            return;
+        m_tree->_clear_key(m_id);
+    }
+
+    inline void clear_val()
+    {
+        if(is_seed())
+            return;
+        m_tree->_clear_val(m_id);
+    }
+
+    inline void clear_children()
+    {
+        if(is_seed())
+            return;
+        m_tree->remove_children(m_id);
+    }
+
+    void create() { _apply_seed(); }
+
+    inline void operator= (NodeType_e t)
+    {
+        _apply_seed();
+        m_tree->_add_flags(m_id, t);
+    }
+
+    inline void operator|= (NodeType_e t)
+    {
+        _apply_seed();
+        m_tree->_add_flags(m_id, t);
+    }
+
+    inline void operator= (NodeInit const& v)
+    {
+        _apply_seed();
+        _apply(v);
+    }
+
+    inline void operator= (NodeScalar const& v)
+    {
+        _apply_seed();
+        _apply(v);
+    }
+
+    inline void operator= (std::nullptr_t)
+    {
+        _apply_seed();
+        _apply(csubstr{});
+    }
+
+    inline void operator= (csubstr v)
+    {
+        _apply_seed();
+        _apply(v);
+    }
+
+    template<size_t N>
+    inline void operator= (const char (&v)[N])
+    {
+        _apply_seed();
+        csubstr sv;
+        sv.assign<N>(v);
+        _apply(sv);
+    }
+
+    /** @} */
+
+public:
+
+    /** @name serialization */
+    /** @{ */
+
+    /** serialize a variable to the arena */
+    template<class T>
+    inline csubstr to_arena(T const& C4_RESTRICT s)
+    {
+        _C4RV();
+        return m_tree->to_arena(s);
+    }
+
+    /** serialize a variable, then assign the result to the node's val */
+    inline NodeRef& operator<< (csubstr s)
+    {
+        // this overload is needed to prevent ambiguity (there's also
+        // operator<< for writing a substr to a stream)
+        _apply_seed();
+        write(this, s);
+        RYML_ASSERT(val() == s);
+        return *this;
+    }
+
+    template<class T>
+    inline NodeRef& operator<< (T const& C4_RESTRICT v)
+    {
+        _apply_seed();
+        write(this, v);
+        return *this;
+    }
+
+    /** serialize a variable, then assign the result to the node's key */
+    template<class T>
+    inline NodeRef& operator<< (Key<const T> const& C4_RESTRICT v)
+    {
+        _apply_seed();
+        set_key_serialized(v.k);
+        return *this;
+    }
+
+    /** serialize a variable, then assign the result to the node's key */
+    template<class T>
+    inline NodeRef& operator<< (Key<T> const& C4_RESTRICT v)
+    {
+        _apply_seed();
+        set_key_serialized(v.k);
+        return *this;
+    }
+
+    NodeRef& operator<< (Key<fmt::const_base64_wrapper> w)
+    {
+        set_key_serialized(w.wrapper);
+        return *this;
+    }
+
+    NodeRef& operator<< (fmt::const_base64_wrapper w)
+    {
+        set_val_serialized(w);
+        return *this;
+    }
+
+    /** @} */
+
+private:
+
+    void _apply_seed()
+    {
+        if(m_seed.str) // we have a seed key: use it to create the new child
+        {
+            //RYML_ASSERT(i.key.scalar.empty() || m_key == i.key.scalar || m_key.empty());
+            m_id = m_tree->append_child(m_id);
+            m_tree->_set_key(m_id, m_seed);
+            m_seed.str = nullptr;
+            m_seed.len = NONE;
+        }
+        else if(m_seed.len != NONE) // we have a seed index: create a child at that position
+        {
+            RYML_ASSERT(m_tree->num_children(m_id) == m_seed.len);
+            m_id = m_tree->append_child(m_id);
+            m_seed.str = nullptr;
+            m_seed.len = NONE;
+        }
+        else
+        {
+            RYML_ASSERT(valid());
+        }
+    }
+
+    inline void _apply(csubstr v)
+    {
+        m_tree->_set_val(m_id, v);
+    }
+
+    inline void _apply(NodeScalar const& v)
+    {
+        m_tree->_set_val(m_id, v);
+    }
+
+    inline void _apply(NodeInit const& i)
+    {
+        m_tree->_set(m_id, i);
+    }
+
+public:
+
+    /** @name modification of hierarchy */
+    /** @{ */
+
+    inline NodeRef insert_child(NodeRef after)
+    {
+        _C4RV();
+        RYML_ASSERT(after.m_tree == m_tree);
+        NodeRef r(m_tree, m_tree->insert_child(m_id, after.m_id));
+        return r;
+    }
+
+    inline NodeRef insert_child(NodeInit const& i, NodeRef after)
+    {
+        _C4RV();
+        RYML_ASSERT(after.m_tree == m_tree);
+        NodeRef r(m_tree, m_tree->insert_child(m_id, after.m_id));
+        r._apply(i);
+        return r;
+    }
+
+    inline NodeRef prepend_child()
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->insert_child(m_id, NONE));
+        return r;
+    }
+
+    inline NodeRef prepend_child(NodeInit const& i)
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->insert_child(m_id, NONE));
+        r._apply(i);
+        return r;
+    }
+
+    inline NodeRef append_child()
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->append_child(m_id));
+        return r;
+    }
+
+    inline NodeRef append_child(NodeInit const& i)
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->append_child(m_id));
+        r._apply(i);
+        return r;
+    }
+
+public:
+
+    inline NodeRef insert_sibling(ConstNodeRef const& after)
+    {
+        _C4RV();
+        RYML_ASSERT(after.m_tree == m_tree);
+        NodeRef r(m_tree, m_tree->insert_sibling(m_id, after.m_id));
+        return r;
+    }
+
+    inline NodeRef insert_sibling(NodeInit const& i, ConstNodeRef const& after)
+    {
+        _C4RV();
+        RYML_ASSERT(after.m_tree == m_tree);
+        NodeRef r(m_tree, m_tree->insert_sibling(m_id, after.m_id));
+        r._apply(i);
+        return r;
+    }
+
+    inline NodeRef prepend_sibling()
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->prepend_sibling(m_id));
+        return r;
+    }
+
+    inline NodeRef prepend_sibling(NodeInit const& i)
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->prepend_sibling(m_id));
+        r._apply(i);
+        return r;
+    }
+
+    inline NodeRef append_sibling()
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->append_sibling(m_id));
+        return r;
+    }
+
+    inline NodeRef append_sibling(NodeInit const& i)
+    {
+        _C4RV();
+        NodeRef r(m_tree, m_tree->append_sibling(m_id));
+        r._apply(i);
+        return r;
+    }
+
+public:
+
+    inline void remove_child(NodeRef & child)
+    {
+        _C4RV();
+        RYML_ASSERT(has_child(child));
+        RYML_ASSERT(child.parent().id() == id());
+        m_tree->remove(child.id());
+        child.clear();
+    }
+
+    //! remove the nth child of this node
+    inline void remove_child(size_t pos)
+    {
+        _C4RV();
+        RYML_ASSERT(pos >= 0 && pos < num_children());
+        size_t child = m_tree->child(m_id, pos);
+        RYML_ASSERT(child != NONE);
+        m_tree->remove(child);
+    }
+
+    //! remove a child by name
+    inline void remove_child(csubstr key)
+    {
+        _C4RV();
+        size_t child = m_tree->find_child(m_id, key);
+        RYML_ASSERT(child != NONE);
+        m_tree->remove(child);
+    }
+
+public:
+
+    /** change the node's position within its parent, placing it after
+     * @p after. To move to the first position in the parent, simply
+     * pass an empty or default-constructed reference like this:
+     * `n.move({})`. */
+    inline void move(ConstNodeRef const& after)
+    {
+        _C4RV();
+        m_tree->move(m_id, after.m_id);
+    }
+
+    /** move the node to a different @p parent (which may belong to a
+     * different tree), placing it after @p after. When the
+     * destination parent is in a new tree, then this node's tree
+     * pointer is reset to the tree of the parent node. */
+    inline void move(NodeRef const& parent, ConstNodeRef const& after)
+    {
+        _C4RV();
+        if(parent.m_tree == m_tree)
+        {
+            m_tree->move(m_id, parent.m_id, after.m_id);
+        }
+        else
+        {
+            parent.m_tree->move(m_tree, m_id, parent.m_id, after.m_id);
+            m_tree = parent.m_tree;
+        }
+    }
+
+    /** duplicate the current node somewhere within its parent, and
+     * place it after the node @p after. To place into the first
+     * position of the parent, simply pass an empty or
+     * default-constructed reference like this: `n.move({})`. */
+    inline NodeRef duplicate(ConstNodeRef const& after) const
+    {
+        _C4RV();
+        RYML_ASSERT(m_tree == after.m_tree || after.m_id == NONE);
+        size_t dup = m_tree->duplicate(m_id, m_tree->parent(m_id), after.m_id);
+        NodeRef r(m_tree, dup);
+        return r;
+    }
+
+    /** duplicate the current node somewhere into a different @p parent
+     * (possibly from a different tree), and place it after the node
+     * @p after. To place into the first position of the parent,
+     * simply pass an empty or default-constructed reference like
+     * this: `n.move({})`. */
+    inline NodeRef duplicate(NodeRef const& parent, ConstNodeRef const& after) const
+    {
+        _C4RV();
+        RYML_ASSERT(parent.m_tree == after.m_tree || after.m_id == NONE);
+        if(parent.m_tree == m_tree)
+        {
+            size_t dup = m_tree->duplicate(m_id, parent.m_id, after.m_id);
+            NodeRef r(m_tree, dup);
+            return r;
+        }
+        else
+        {
+            size_t dup = parent.m_tree->duplicate(m_tree, m_id, parent.m_id, after.m_id);
+            NodeRef r(parent.m_tree, dup);
+            return r;
+        }
+    }
+
+    inline void duplicate_children(NodeRef const& parent, ConstNodeRef const& after) const
+    {
+        _C4RV();
+        RYML_ASSERT(parent.m_tree == after.m_tree);
+        if(parent.m_tree == m_tree)
+        {
+            m_tree->duplicate_children(m_id, parent.m_id, after.m_id);
+        }
+        else
+        {
+            parent.m_tree->duplicate_children(m_tree, m_id, parent.m_id, after.m_id);
+        }
+    }
+
+    /** @} */
+
+#undef _C4RV
+};
+
+
+//-----------------------------------------------------------------------------
+
+inline ConstNodeRef::ConstNodeRef(NodeRef const& that)
+    : m_tree(that.m_tree)
+    , m_id(!that.is_seed() ? that.id() : NONE)
+{
+}
+
+inline ConstNodeRef::ConstNodeRef(NodeRef && that)
+    : m_tree(that.m_tree)
+    , m_id(!that.is_seed() ? that.id() : NONE)
+{
+}
+
+
+inline ConstNodeRef& ConstNodeRef::operator= (NodeRef const& that)
+{
+    m_tree = (that.m_tree);
+    m_id = (!that.is_seed() ? that.id() : NONE);
+    return *this;
+}
+
+inline ConstNodeRef& ConstNodeRef::operator= (NodeRef && that)
+{
+    m_tree = (that.m_tree);
+    m_id = (!that.is_seed() ? that.id() : NONE);
+    return *this;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<class T>
+inline void write(NodeRef *n, T const& v)
+{
+    n->set_val_serialized(v);
+}
+
+template<class T>
+typename std::enable_if< ! std::is_floating_point<T>::value, bool>::type
+inline read(NodeRef const& n, T *v)
+{
+    return from_chars(n.val(), v);
+}
+template<class T>
+typename std::enable_if< ! std::is_floating_point<T>::value, bool>::type
+inline read(ConstNodeRef const& n, T *v)
+{
+    return from_chars(n.val(), v);
+}
+
+template<class T>
+typename std::enable_if<std::is_floating_point<T>::value, bool>::type
+inline read(NodeRef const& n, T *v)
+{
+    return from_chars_float(n.val(), v);
+}
+template<class T>
+typename std::enable_if<std::is_floating_point<T>::value, bool>::type
+inline read(ConstNodeRef const& n, T *v)
+{
+    return from_chars_float(n.val(), v);
+}
+
+
+} // namespace yml
+} // namespace c4
+
+
+#if defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+#ifdef __GNUC__
+#   pragma GCC diagnostic pop
+#endif
+
+#endif /* _C4_YML_NODE_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/parse.cpp b/thirdparty/ryml/src/c4/yml/parse.cpp
new file mode 100644
index 000000000..7b038e672
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/parse.cpp
@@ -0,0 +1,5724 @@
+#include "c4/yml/parse.hpp"
+#include "c4/error.hpp"
+#include "c4/utf.hpp"
+#include <c4/dump.hpp>
+
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdio.h>
+
+#include "c4/yml/detail/parser_dbg.hpp"
+#ifdef RYML_DBG
+#include "c4/yml/detail/print.hpp"
+#endif
+
+#ifndef RYML_ERRMSG_SIZE
+    #define RYML_ERRMSG_SIZE 1024
+#endif
+
+//#define RYML_WITH_TAB_TOKENS
+#ifdef RYML_WITH_TAB_TOKENS
+#define _RYML_WITH_TAB_TOKENS(...) __VA_ARGS__
+#define _RYML_WITH_OR_WITHOUT_TAB_TOKENS(with, without) with
+#else
+#define _RYML_WITH_TAB_TOKENS(...)
+#define _RYML_WITH_OR_WITHOUT_TAB_TOKENS(with, without) without
+#endif
+
+
+#if defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4296/*expression is always 'boolean_value'*/)
+#elif defined(__clang__)
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wtype-limits" // to remove a warning on an assertion that a size_t >= 0. Later on, this size_t will turn into a template argument, and then it can become < 0.
+#   pragma clang diagnostic ignored "-Wformat-nonliteral"
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wtype-limits" // to remove a warning on an assertion that a size_t >= 0. Later on, this size_t will turn into a template argument, and then it can become < 0.
+#   pragma GCC diagnostic ignored "-Wformat-nonliteral"
+#   if __GNUC__ >= 7
+#       pragma GCC diagnostic ignored "-Wduplicated-branches"
+#   endif
+#endif
+
+namespace c4 {
+namespace yml {
+
+namespace {
+
+template<class DumpFn, class ...Args>
+void _parse_dump(DumpFn dumpfn, c4::csubstr fmt, Args&& ...args)
+{
+    char writebuf[256];
+    auto results = c4::format_dump_resume(dumpfn, writebuf, fmt, std::forward<Args>(args)...);
+    // resume writing if the results failed to fit the buffer
+    if(C4_UNLIKELY(results.bufsize > sizeof(writebuf))) // bufsize will be that of the largest element serialized. Eg int(1), will require 1 byte.
+    {
+        results = format_dump_resume(dumpfn, results, writebuf, fmt, std::forward<Args>(args)...);
+        if(C4_UNLIKELY(results.bufsize > sizeof(writebuf)))
+        {
+            results = format_dump_resume(dumpfn, results, writebuf, fmt, std::forward<Args>(args)...);
+        }
+    }
+}
+
+bool _is_scalar_next__runk(csubstr s)
+{
+    return !(s.begins_with(": ") || s.begins_with_any("#,{}[]%&") || s.begins_with("? ") || s == "-" || s.begins_with("- ") || s.begins_with(":\"") || s.begins_with(":'"));
+}
+
+bool _is_scalar_next__rseq_rval(csubstr s)
+{
+    return !(s.begins_with_any("[{!&") || s.begins_with("? ") || s.begins_with("- ") || s == "-");
+}
+
+bool _is_scalar_next__rmap(csubstr s)
+{
+    return !(s.begins_with(": ") || s.begins_with_any("#,!&") || s.begins_with("? ") _RYML_WITH_TAB_TOKENS(|| s.begins_with(":\t")));
+}
+
+bool _is_scalar_next__rmap_val(csubstr s)
+{
+    return !(s.begins_with("- ") || s.begins_with_any("{[") || s == "-");
+}
+
+bool _is_doc_sep(csubstr s)
+{
+    constexpr const csubstr dashes = "---";
+    constexpr const csubstr ellipsis = "...";
+    constexpr const csubstr whitesp = " \t";
+    if(s.begins_with(dashes))
+        return s == dashes || s.sub(3).begins_with_any(whitesp);
+    else if(s.begins_with(ellipsis))
+        return s == ellipsis || s.sub(3).begins_with_any(whitesp);
+    return false;
+}
+
+/** @p i is set to the first non whitespace character after the line
+ * @return the number of empty lines after the initial position */
+size_t count_following_newlines(csubstr r, size_t *C4_RESTRICT i, size_t indentation)
+{
+    RYML_ASSERT(r[*i] == '\n');
+    size_t numnl_following = 0;
+    ++(*i);
+    for( ; *i < r.len; ++(*i))
+    {
+        if(r.str[*i] == '\n')
+        {
+            ++numnl_following;
+            if(indentation) // skip the indentation after the newline
+            {
+                size_t stop = *i + indentation;
+                for( ; *i < r.len; ++(*i))
+                {
+                    if(r.str[*i] != ' ' && r.str[*i] != '\r')
+                        break;
+                    RYML_ASSERT(*i < stop);
+                }
+                C4_UNUSED(stop);
+            }
+        }
+        else if(r.str[*i] == ' ' || r.str[*i] == '\t' || r.str[*i] == '\r')  // skip leading whitespace
+            ;
+        else
+            break;
+    }
+    return numnl_following;
+}
+
+} // anon namespace
+
+
+//-----------------------------------------------------------------------------
+
+Parser::~Parser()
+{
+    _free();
+    _clr();
+}
+
+Parser::Parser(Callbacks const& cb, ParserOptions opts)
+    : m_options(opts)
+    , m_file()
+    , m_buf()
+    , m_root_id(NONE)
+    , m_tree()
+    , m_stack(cb)
+    , m_state()
+    , m_key_tag_indentation(0)
+    , m_key_tag2_indentation(0)
+    , m_key_tag()
+    , m_key_tag2()
+    , m_val_tag_indentation(0)
+    , m_val_tag()
+    , m_key_anchor_was_before(false)
+    , m_key_anchor_indentation(0)
+    , m_key_anchor()
+    , m_val_anchor_indentation(0)
+    , m_val_anchor()
+    , m_filter_arena()
+    , m_newline_offsets()
+    , m_newline_offsets_size(0)
+    , m_newline_offsets_capacity(0)
+    , m_newline_offsets_buf()
+{
+    m_stack.push(State{});
+    m_state = &m_stack.top();
+}
+
+Parser::Parser(Parser &&that)
+    : m_options(that.m_options)
+    , m_file(that.m_file)
+    , m_buf(that.m_buf)
+    , m_root_id(that.m_root_id)
+    , m_tree(that.m_tree)
+    , m_stack(std::move(that.m_stack))
+    , m_state(&m_stack.top())
+    , m_key_tag_indentation(that.m_key_tag_indentation)
+    , m_key_tag2_indentation(that.m_key_tag2_indentation)
+    , m_key_tag(that.m_key_tag)
+    , m_key_tag2(that.m_key_tag2)
+    , m_val_tag_indentation(that.m_val_tag_indentation)
+    , m_val_tag(that.m_val_tag)
+    , m_key_anchor_was_before(that.m_key_anchor_was_before)
+    , m_key_anchor_indentation(that.m_key_anchor_indentation)
+    , m_key_anchor(that.m_key_anchor)
+    , m_val_anchor_indentation(that.m_val_anchor_indentation)
+    , m_val_anchor(that.m_val_anchor)
+    , m_filter_arena(that.m_filter_arena)
+    , m_newline_offsets(that.m_newline_offsets)
+    , m_newline_offsets_size(that.m_newline_offsets_size)
+    , m_newline_offsets_capacity(that.m_newline_offsets_capacity)
+    , m_newline_offsets_buf(that.m_newline_offsets_buf)
+{
+    that._clr();
+}
+
+Parser::Parser(Parser const& that)
+    : m_options(that.m_options)
+    , m_file(that.m_file)
+    , m_buf(that.m_buf)
+    , m_root_id(that.m_root_id)
+    , m_tree(that.m_tree)
+    , m_stack(that.m_stack)
+    , m_state(&m_stack.top())
+    , m_key_tag_indentation(that.m_key_tag_indentation)
+    , m_key_tag2_indentation(that.m_key_tag2_indentation)
+    , m_key_tag(that.m_key_tag)
+    , m_key_tag2(that.m_key_tag2)
+    , m_val_tag_indentation(that.m_val_tag_indentation)
+    , m_val_tag(that.m_val_tag)
+    , m_key_anchor_was_before(that.m_key_anchor_was_before)
+    , m_key_anchor_indentation(that.m_key_anchor_indentation)
+    , m_key_anchor(that.m_key_anchor)
+    , m_val_anchor_indentation(that.m_val_anchor_indentation)
+    , m_val_anchor(that.m_val_anchor)
+    , m_filter_arena()
+    , m_newline_offsets()
+    , m_newline_offsets_size()
+    , m_newline_offsets_capacity()
+    , m_newline_offsets_buf()
+{
+    if(that.m_newline_offsets_capacity)
+    {
+        _resize_locations(that.m_newline_offsets_capacity);
+        _RYML_CB_CHECK(m_stack.m_callbacks, m_newline_offsets_capacity == that.m_newline_offsets_capacity);
+        memcpy(m_newline_offsets, that.m_newline_offsets, that.m_newline_offsets_size * sizeof(size_t));
+        m_newline_offsets_size = that.m_newline_offsets_size;
+    }
+    if(that.m_filter_arena.len)
+    {
+        _resize_filter_arena(that.m_filter_arena.len);
+    }
+}
+
+Parser& Parser::operator=(Parser &&that)
+{
+    _free();
+    m_options = (that.m_options);
+    m_file = (that.m_file);
+    m_buf = (that.m_buf);
+    m_root_id = (that.m_root_id);
+    m_tree = (that.m_tree);
+    m_stack = std::move(that.m_stack);
+    m_state = (&m_stack.top());
+    m_key_tag_indentation = (that.m_key_tag_indentation);
+    m_key_tag2_indentation = (that.m_key_tag2_indentation);
+    m_key_tag = (that.m_key_tag);
+    m_key_tag2 = (that.m_key_tag2);
+    m_val_tag_indentation = (that.m_val_tag_indentation);
+    m_val_tag = (that.m_val_tag);
+    m_key_anchor_was_before = (that.m_key_anchor_was_before);
+    m_key_anchor_indentation = (that.m_key_anchor_indentation);
+    m_key_anchor = (that.m_key_anchor);
+    m_val_anchor_indentation = (that.m_val_anchor_indentation);
+    m_val_anchor = (that.m_val_anchor);
+    m_filter_arena = that.m_filter_arena;
+    m_newline_offsets = (that.m_newline_offsets);
+    m_newline_offsets_size = (that.m_newline_offsets_size);
+    m_newline_offsets_capacity = (that.m_newline_offsets_capacity);
+    m_newline_offsets_buf = (that.m_newline_offsets_buf);
+    that._clr();
+    return *this;
+}
+
+Parser& Parser::operator=(Parser const& that)
+{
+    _free();
+    m_options = (that.m_options);
+    m_file = (that.m_file);
+    m_buf = (that.m_buf);
+    m_root_id = (that.m_root_id);
+    m_tree = (that.m_tree);
+    m_stack = that.m_stack;
+    m_state = &m_stack.top();
+    m_key_tag_indentation = (that.m_key_tag_indentation);
+    m_key_tag2_indentation = (that.m_key_tag2_indentation);
+    m_key_tag = (that.m_key_tag);
+    m_key_tag2 = (that.m_key_tag2);
+    m_val_tag_indentation = (that.m_val_tag_indentation);
+    m_val_tag = (that.m_val_tag);
+    m_key_anchor_was_before = (that.m_key_anchor_was_before);
+    m_key_anchor_indentation = (that.m_key_anchor_indentation);
+    m_key_anchor = (that.m_key_anchor);
+    m_val_anchor_indentation = (that.m_val_anchor_indentation);
+    m_val_anchor = (that.m_val_anchor);
+    if(that.m_filter_arena.len > 0)
+        _resize_filter_arena(that.m_filter_arena.len);
+    if(that.m_newline_offsets_capacity > m_newline_offsets_capacity)
+        _resize_locations(that.m_newline_offsets_capacity);
+    _RYML_CB_CHECK(m_stack.m_callbacks, m_newline_offsets_capacity >= that.m_newline_offsets_capacity);
+    _RYML_CB_CHECK(m_stack.m_callbacks, m_newline_offsets_capacity >= that.m_newline_offsets_size);
+    memcpy(m_newline_offsets, that.m_newline_offsets, that.m_newline_offsets_size * sizeof(size_t));
+    m_newline_offsets_size = that.m_newline_offsets_size;
+    m_newline_offsets_buf = that.m_newline_offsets_buf;
+    return *this;
+}
+
+void Parser::_clr()
+{
+    m_options = {};
+    m_file = {};
+    m_buf = {};
+    m_root_id = {};
+    m_tree = {};
+    m_stack.clear();
+    m_state = {};
+    m_key_tag_indentation = {};
+    m_key_tag2_indentation = {};
+    m_key_tag = {};
+    m_key_tag2 = {};
+    m_val_tag_indentation = {};
+    m_val_tag = {};
+    m_key_anchor_was_before = {};
+    m_key_anchor_indentation = {};
+    m_key_anchor = {};
+    m_val_anchor_indentation = {};
+    m_val_anchor = {};
+    m_filter_arena = {};
+    m_newline_offsets = {};
+    m_newline_offsets_size = {};
+    m_newline_offsets_capacity = {};
+    m_newline_offsets_buf = {};
+}
+
+void Parser::_free()
+{
+    if(m_newline_offsets)
+    {
+        _RYML_CB_FREE(m_stack.m_callbacks, m_newline_offsets, size_t, m_newline_offsets_capacity);
+        m_newline_offsets = nullptr;
+        m_newline_offsets_size = 0u;
+        m_newline_offsets_capacity = 0u;
+        m_newline_offsets_buf = 0u;
+    }
+    if(m_filter_arena.len)
+    {
+        _RYML_CB_FREE(m_stack.m_callbacks, m_filter_arena.str, char, m_filter_arena.len);
+        m_filter_arena = {};
+    }
+    m_stack._free();
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_reset()
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_stack.size() == 1);
+    m_stack.clear();
+    m_stack.push({});
+    m_state = &m_stack.top();
+    m_state->reset(m_file.str, m_root_id);
+
+    m_key_tag_indentation = 0;
+    m_key_tag2_indentation = 0;
+    m_key_tag.clear();
+    m_key_tag2.clear();
+    m_val_tag_indentation = 0;
+    m_val_tag.clear();
+    m_key_anchor_was_before = false;
+    m_key_anchor_indentation = 0;
+    m_key_anchor.clear();
+    m_val_anchor_indentation = 0;
+    m_val_anchor.clear();
+
+    if(m_options.locations())
+    {
+        _prepare_locations();
+    }
+}
+
+//-----------------------------------------------------------------------------
+template<class DumpFn>
+void Parser::_fmt_msg(DumpFn &&dumpfn) const
+{
+    auto const& lc = m_state->line_contents;
+    csubstr contents = lc.stripped;
+    if(contents.len)
+    {
+        // print the yaml src line
+        size_t offs = 3u + to_chars(substr{}, m_state->pos.line) + to_chars(substr{}, m_state->pos.col);
+        if(m_file.len)
+        {
+            _parse_dump(dumpfn, "{}:", m_file);
+            offs += m_file.len + 1;
+        }
+        _parse_dump(dumpfn, "{}:{}: ", m_state->pos.line, m_state->pos.col);
+        csubstr maybe_full_content = (contents.len < 80u ? contents : contents.first(80u));
+        csubstr maybe_ellipsis = (contents.len < 80u ? csubstr{} : csubstr("..."));
+        _parse_dump(dumpfn, "{}{}  (size={})\n", maybe_full_content, maybe_ellipsis, contents.len);
+        // highlight the remaining portion of the previous line
+        size_t firstcol = (size_t)(lc.rem.begin() - lc.full.begin());
+        size_t lastcol = firstcol + lc.rem.len;
+        for(size_t i = 0; i < offs + firstcol; ++i)
+            dumpfn(" ");
+        dumpfn("^");
+        for(size_t i = 1, e = (lc.rem.len < 80u ? lc.rem.len : 80u); i < e; ++i)
+            dumpfn("~");
+        _parse_dump(dumpfn, "{}  (cols {}-{})\n", maybe_ellipsis, firstcol+1, lastcol+1);
+    }
+    else
+    {
+        dumpfn("\n");
+    }
+
+#ifdef RYML_DBG
+    // next line: print the state flags
+    {
+        char flagbuf_[64];
+        _parse_dump(dumpfn, "top state: {}\n", _prfl(flagbuf_, m_state->flags));
+    }
+#endif
+}
+
+
+//-----------------------------------------------------------------------------
+template<class ...Args>
+void Parser::_err(csubstr fmt, Args const& C4_RESTRICT ...args) const
+{
+    char errmsg[RYML_ERRMSG_SIZE];
+    detail::_SubstrWriter writer(errmsg);
+    auto dumpfn = [&writer](csubstr s){ writer.append(s); };
+    _parse_dump(dumpfn, fmt, args...);
+    writer.append('\n');
+    _fmt_msg(dumpfn);
+    size_t len = writer.pos < RYML_ERRMSG_SIZE ? writer.pos : RYML_ERRMSG_SIZE;
+    m_tree->m_callbacks.m_error(errmsg, len, m_state->pos, m_tree->m_callbacks.m_user_data);
+}
+
+//-----------------------------------------------------------------------------
+#ifdef RYML_DBG
+template<class ...Args>
+void Parser::_dbg(csubstr fmt, Args const& C4_RESTRICT ...args) const
+{
+    auto dumpfn = [](csubstr s){ fwrite(s.str, 1, s.len, stdout); };
+    _parse_dump(dumpfn, fmt, args...);
+    dumpfn("\n");
+    _fmt_msg(dumpfn);
+}
+#endif
+
+//-----------------------------------------------------------------------------
+bool Parser::_finished_file() const
+{
+    bool ret = m_state->pos.offset >= m_buf.len;
+    if(ret)
+    {
+        _c4dbgp("finished file!!!");
+    }
+    return ret;
+}
+
+//-----------------------------------------------------------------------------
+bool Parser::_finished_line() const
+{
+    return m_state->line_contents.rem.empty();
+}
+
+//-----------------------------------------------------------------------------
+void Parser::parse_in_place(csubstr file, substr buf, Tree *t, size_t node_id)
+{
+    m_file = file;
+    m_buf = buf;
+    m_root_id = node_id;
+    m_tree = t;
+    _reset();
+    while( ! _finished_file())
+    {
+        _scan_line();
+        while( ! _finished_line())
+            _handle_line();
+        if(_finished_file())
+            break; // it may have finished because of multiline blocks
+        _line_ended();
+    }
+    _handle_finished_file();
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_handle_finished_file()
+{
+    _end_stream();
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_handle_line()
+{
+    _c4dbgq("\n-----------");
+    _c4dbgt("handling line={}, offset={}B", m_state->pos.line, m_state->pos.offset);
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! m_state->line_contents.rem.empty());
+    if(has_any(RSEQ))
+    {
+        if(has_any(FLOW))
+        {
+            if(_handle_seq_flow())
+                return;
+        }
+        else
+        {
+            if(_handle_seq_blck())
+                return;
+        }
+    }
+    else if(has_any(RMAP))
+    {
+        if(has_any(FLOW))
+        {
+            if(_handle_map_flow())
+                return;
+        }
+        else
+        {
+            if(_handle_map_blck())
+                return;
+        }
+    }
+    else if(has_any(RUNK))
+    {
+        if(_handle_unk())
+            return;
+    }
+
+    if(_handle_top())
+        return;
+}
+
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_unk()
+{
+    _c4dbgp("handle_unk");
+
+    csubstr rem = m_state->line_contents.rem;
+    const bool start_as_child = (node(m_state) == nullptr);
+
+    if(C4_UNLIKELY(has_any(NDOC)))
+    {
+        if(rem == "---" || rem.begins_with("--- "))
+        {
+            _start_new_doc(rem);
+            return true;
+        }
+        auto trimmed = rem.triml(' ');
+        if(trimmed == "---" || trimmed.begins_with("--- "))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, rem.len >= trimmed.len);
+            _line_progressed(rem.len - trimmed.len);
+            _start_new_doc(trimmed);
+            _save_indentation();
+            return true;
+        }
+        else if(trimmed.begins_with("..."))
+        {
+            _end_stream();
+        }
+        else if(trimmed.first_of("#%") == csubstr::npos) // neither a doc nor a tag
+        {
+            _c4dbgpf("starting implicit doc to accomodate unexpected tokens: '{}'", rem);
+            size_t indref = m_state->indref;
+            _push_level();
+            _start_doc();
+            _set_indentation(indref);
+        }
+        _RYML_CB_ASSERT(m_stack.m_callbacks, !trimmed.empty());
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT|RSEQ|RMAP));
+    if(m_state->indref > 0)
+    {
+        csubstr ws = rem.left_of(rem.first_not_of(' '));
+        if(m_state->indref <= ws.len)
+        {
+            _c4dbgpf("skipping base indentation of {}", m_state->indref);
+            _line_progressed(m_state->indref);
+            rem = rem.sub(m_state->indref);
+        }
+    }
+
+    if(rem.begins_with("- ") _RYML_WITH_TAB_TOKENS( || rem.begins_with("-\t")))
+    {
+        _c4dbgpf("it's a seq (as_child={})", start_as_child);
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level();
+        _start_seq(start_as_child);
+        _save_indentation();
+        _line_progressed(2);
+        return true;
+    }
+    else if(rem == '-')
+    {
+        _c4dbgpf("it's a seq (as_child={})", start_as_child);
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level();
+        _start_seq(start_as_child);
+        _save_indentation();
+        _line_progressed(1);
+        return true;
+    }
+    else if(rem.begins_with('['))
+    {
+        _c4dbgpf("it's a seq, flow (as_child={})", start_as_child);
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level(/*explicit flow*/true);
+        _start_seq(start_as_child);
+        add_flags(FLOW);
+        _line_progressed(1);
+        return true;
+    }
+    else if(rem.begins_with('{'))
+    {
+        _c4dbgpf("it's a map, flow (as_child={})", start_as_child);
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level(/*explicit flow*/true);
+        _start_map(start_as_child);
+        addrem_flags(FLOW|RKEY, RVAL);
+        _line_progressed(1);
+        return true;
+    }
+    else if(rem.begins_with("? "))
+    {
+        _c4dbgpf("it's a map (as_child={}) + this key is complex", start_as_child);
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level();
+        _start_map(start_as_child);
+        addrem_flags(RKEY|QMRK, RVAL);
+        _save_indentation();
+        _line_progressed(2);
+        return true;
+    }
+    else if(rem.begins_with(": ") && !has_all(SSCL))
+    {
+        _c4dbgp("it's a map with an empty key");
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level();
+        _start_map(start_as_child);
+        _store_scalar_null(rem.str);
+        addrem_flags(RVAL, RKEY);
+        _save_indentation();
+        _line_progressed(2);
+        return true;
+    }
+    else if(rem == ':' && !has_all(SSCL))
+    {
+        _c4dbgp("it's a map with an empty key");
+        _move_key_anchor_to_val_anchor();
+        _move_key_tag_to_val_tag();
+        _push_level();
+        _start_map(start_as_child);
+        _store_scalar_null(rem.str);
+        addrem_flags(RVAL, RKEY);
+        _save_indentation();
+        _line_progressed(1);
+        return true;
+    }
+    else if(_handle_types())
+    {
+        return true;
+    }
+    else if(!rem.begins_with('*') && _handle_key_anchors_and_refs())
+    {
+        return true;
+    }
+    else if(has_all(SSCL))
+    {
+        _c4dbgpf("there's a stored scalar: '{}'", m_state->scalar);
+
+        csubstr saved_scalar;
+        bool is_quoted;
+        if(_scan_scalar_unk(&saved_scalar, &is_quoted))
+        {
+            rem = m_state->line_contents.rem;
+            _c4dbgpf("... and there's also a scalar next! '{}'", saved_scalar);
+            if(rem.begins_with_any(" \t"))
+            {
+                size_t n = rem.first_not_of(" \t");
+                _c4dbgpf("skipping {} spaces/tabs", n);
+                rem = rem.sub(n);
+                _line_progressed(n);
+            }
+        }
+
+        _c4dbgpf("rem='{}'", rem);
+
+        if(rem.begins_with(", "))
+        {
+            _c4dbgpf("got a ',' -- it's a seq (as_child={})", start_as_child);
+            _start_seq(start_as_child);
+            add_flags(FLOW);
+            _append_val(_consume_scalar());
+            _line_progressed(2);
+        }
+        else if(rem.begins_with(','))
+        {
+            _c4dbgpf("got a ',' -- it's a seq (as_child={})", start_as_child);
+            _start_seq(start_as_child);
+            add_flags(FLOW);
+            _append_val(_consume_scalar());
+            _line_progressed(1);
+        }
+        else if(rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+        {
+            _c4dbgpf("got a ': ' -- it's a map (as_child={})", start_as_child);
+            _start_map_unk(start_as_child); // wait for the val scalar to append the key-val pair
+            _line_progressed(2);
+        }
+        else if(rem == ":" || rem.begins_with(":\"") || rem.begins_with(":'"))
+        {
+            if(rem == ":") { _c4dbgpf("got a ':' -- it's a map (as_child={})", start_as_child); }
+            else { _c4dbgpf("got a '{}' -- it's a map (as_child={})", rem.first(2), start_as_child); }
+            _start_map_unk(start_as_child); // wait for the val scalar to append the key-val pair
+            _line_progressed(1); // advance only 1
+        }
+        else if(rem.begins_with('}'))
+        {
+            if(!has_all(RMAP|FLOW))
+            {
+                _c4err("invalid token: not reading a map");
+            }
+            if(!has_all(SSCL))
+            {
+                _c4err("no scalar stored");
+            }
+            _append_key_val(saved_scalar);
+            _stop_map();
+            _line_progressed(1);
+        }
+        else if(rem.begins_with("..."))
+        {
+            _c4dbgp("got stream end '...'");
+            _end_stream();
+            _line_progressed(3);
+        }
+        else if(rem.begins_with('#'))
+        {
+            _c4dbgpf("it's a comment: '{}'", rem);
+            _scan_comment();
+            return true;
+        }
+        else if(_handle_key_anchors_and_refs())
+        {
+            return true;
+        }
+        else if(rem.begins_with(" ") || rem.begins_with("\t"))
+        {
+            size_t n = rem.first_not_of(" \t");
+            if(n == npos)
+                n = rem.len;
+            _c4dbgpf("has {} spaces/tabs, skip...", n);
+            _line_progressed(n);
+            return true;
+        }
+        else if(rem.empty())
+        {
+            // nothing to do
+        }
+        else if(rem == "---" || rem.begins_with("--- "))
+        {
+            _c4dbgp("caught ---: starting doc");
+            _start_new_doc(rem);
+            return true;
+        }
+        else if(rem.begins_with('%'))
+        {
+            _c4dbgp("caught a directive: ignoring...");
+            _line_progressed(rem.len);
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+
+        if( ! saved_scalar.empty())
+        {
+            _store_scalar(saved_scalar, is_quoted);
+        }
+
+        return true;
+    }
+    else
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(SSCL));
+        csubstr scalar;
+        size_t indentation = m_state->line_contents.indentation; // save
+        bool is_quoted;
+        if(_scan_scalar_unk(&scalar, &is_quoted))
+        {
+            _c4dbgpf("got a {} scalar", is_quoted ? "quoted" : "");
+            rem = m_state->line_contents.rem;
+            {
+                size_t first = rem.first_not_of(" \t");
+                if(first && first != npos)
+                {
+                    _c4dbgpf("skip {} whitespace characters", first);
+                   _line_progressed(first);
+                   rem = rem.sub(first);
+                }
+            }
+            _store_scalar(scalar, is_quoted);
+            if(rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+            {
+                _c4dbgpf("got a ': ' next -- it's a map (as_child={})", start_as_child);
+                _push_level();
+                _start_map(start_as_child); // wait for the val scalar to append the key-val pair
+                _set_indentation(indentation);
+                _line_progressed(2); // call this AFTER saving the indentation
+            }
+            else if(rem == ":")
+            {
+                _c4dbgpf("got a ':' next -- it's a map (as_child={})", start_as_child);
+                _push_level();
+                _start_map(start_as_child); // wait for the val scalar to append the key-val pair
+                _set_indentation(indentation);
+                _line_progressed(1); // call this AFTER saving the indentation
+            }
+            else
+            {
+                // we still don't know whether it's a seq or a map
+                // so just store the scalar
+            }
+            return true;
+        }
+        else if(rem.begins_with_any(" \t"))
+        {
+            csubstr ws = rem.left_of(rem.first_not_of(" \t"));
+            rem = rem.right_of(ws);
+            if(has_all(RTOP) && rem.begins_with("---"))
+            {
+                _c4dbgp("there's a doc starting, and it's indented");
+                _set_indentation(ws.len);
+            }
+            _c4dbgpf("skipping {} spaces/tabs", ws.len);
+            _line_progressed(ws.len);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+
+//-----------------------------------------------------------------------------
+C4_ALWAYS_INLINE void Parser::_skipchars(char c)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.rem.begins_with(c));
+    size_t pos = m_state->line_contents.rem.first_not_of(c);
+    if(pos == npos)
+        pos = m_state->line_contents.rem.len; // maybe the line is just whitespace
+    _c4dbgpf("skip {} '{}'", pos, c);
+    _line_progressed(pos);
+}
+
+template<size_t N>
+C4_ALWAYS_INLINE void Parser::_skipchars(const char (&chars)[N])
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.rem.begins_with_any(chars));
+    size_t pos = m_state->line_contents.rem.first_not_of(chars);
+    if(pos == npos)
+        pos = m_state->line_contents.rem.len; // maybe the line is just whitespace
+    _c4dbgpf("skip {} characters", pos);
+    _line_progressed(pos);
+}
+
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_seq_flow()
+{
+    _c4dbgpf("handle_seq_flow: node_id={} level={}", m_state->node_id, m_state->level);
+    csubstr rem = m_state->line_contents.rem;
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RSEQ|FLOW));
+
+    if(rem.begins_with(' '))
+    {
+        // with explicit flow, indentation does not matter
+        _c4dbgp("starts with spaces");
+        _skipchars(' ');
+        return true;
+    }
+    _RYML_WITH_TAB_TOKENS(else if(rem.begins_with('\t'))
+    {
+        _c4dbgp("starts with tabs");
+        _skipchars('\t');
+        return true;
+    })
+    else if(rem.begins_with('#'))
+    {
+        _c4dbgp("it's a comment");
+        rem = _scan_comment(); // also progresses the line
+        return true;
+    }
+    else if(rem.begins_with(']'))
+    {
+        _c4dbgp("end the sequence");
+        _pop_level();
+        _line_progressed(1);
+        if(has_all(RSEQIMAP))
+        {
+            _stop_seqimap();
+            _pop_level();
+        }
+        return true;
+    }
+
+    if(has_any(RVAL))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT));
+        bool is_quoted;
+        if(_scan_scalar_seq_flow(&rem, &is_quoted))
+        {
+            _c4dbgp("it's a scalar");
+            addrem_flags(RNXT, RVAL);
+            _append_val(rem, is_quoted);
+            return true;
+        }
+        else if(rem.begins_with('['))
+        {
+            _c4dbgp("val is a child seq");
+            addrem_flags(RNXT, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _start_seq();
+            add_flags(FLOW);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('{'))
+        {
+            _c4dbgp("val is a child map");
+            addrem_flags(RNXT, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _start_map();
+            addrem_flags(FLOW|RKEY, RVAL);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem == ':')
+        {
+            _c4dbgpf("found ':' -- there's an implicit map in the seq node[{}]", m_state->node_id);
+            _start_seqimap();
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+        {
+            _c4dbgpf("found ': ' -- there's an implicit map in the seq node[{}]", m_state->node_id);
+            _start_seqimap();
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem.begins_with("? "))
+        {
+            _c4dbgpf("found '? ' -- there's an implicit map in the seq node[{}]", m_state->node_id);
+            _start_seqimap();
+            _line_progressed(2);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_any(SSCL) && m_state->scalar == "");
+            addrem_flags(QMRK|RKEY, RVAL|SSCL);
+            return true;
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_val_anchors_and_refs())
+        {
+            return true;
+        }
+        else if(rem.begins_with(", "))
+        {
+            _c4dbgp("found ',' -- the value was null");
+            _append_val_null(rem.str - 1);
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem.begins_with(','))
+        {
+            _c4dbgp("found ',' -- the value was null");
+            _append_val_null(rem.str - 1);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('\t'))
+        {
+            _skipchars('\t');
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else if(has_any(RNXT))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+        if(rem.begins_with(", "))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(FLOW));
+            _c4dbgp("seq: expect next val");
+            addrem_flags(RVAL, RNXT);
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem.begins_with(','))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(FLOW));
+            _c4dbgp("seq: expect next val");
+            addrem_flags(RVAL, RNXT);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem == ':')
+        {
+            _c4dbgpf("found ':' -- there's an implicit map in the seq node[{}]", m_state->node_id);
+            _start_seqimap();
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+        {
+            _c4dbgpf("found ': ' -- there's an implicit map in the seq node[{}]", m_state->node_id);
+            _start_seqimap();
+            _line_progressed(2);
+            return true;
+        }
+        else
+        {
+            _c4err("was expecting a comma");
+        }
+    }
+    else
+    {
+        _c4err("internal error");
+    }
+
+    return true;
+}
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_seq_blck()
+{
+    _c4dbgpf("handle_seq_impl: node_id={} level={}", m_state->node_id, m_state->level);
+    csubstr rem = m_state->line_contents.rem;
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RSEQ));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(FLOW));
+
+    if(rem.begins_with('#'))
+    {
+        _c4dbgp("it's a comment");
+        rem = _scan_comment();
+        return true;
+    }
+    if(has_any(RNXT))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+
+        if(_handle_indentation())
+            return true;
+
+        if(rem.begins_with("- ") _RYML_WITH_TAB_TOKENS( || rem.begins_with("-\t")))
+        {
+            _c4dbgp("expect another val");
+            addrem_flags(RVAL, RNXT);
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem == '-')
+        {
+            _c4dbgp("expect another val");
+            addrem_flags(RVAL, RNXT);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with_any(" \t"))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks,  ! _at_line_begin());
+            _skipchars(" \t");
+            return true;
+        }
+        else if(rem.begins_with("..."))
+        {
+            _c4dbgp("got stream end '...'");
+            _end_stream();
+            _line_progressed(3);
+            return true;
+        }
+        else if(rem.begins_with("---"))
+        {
+            _c4dbgp("got document start '---'");
+            _start_new_doc(rem);
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else if(has_any(RVAL))
+    {
+        // there can be empty values
+        if(_handle_indentation())
+            return true;
+
+        csubstr s;
+        bool is_quoted;
+        if(_scan_scalar_seq_blck(&s, &is_quoted)) // this also progresses the line
+        {
+            _c4dbgpf("it's a{} scalar", is_quoted ? " quoted" : "");
+
+            rem = m_state->line_contents.rem;
+            if(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(rem.begins_with_any(" \t"), rem.begins_with(' ')))
+            {
+                _c4dbgp("skipping whitespace...");
+                size_t skip = rem.first_not_of(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+                if(skip == csubstr::npos)
+                    skip = rem.len; // maybe the line is just whitespace
+                _line_progressed(skip);
+                rem = rem.sub(skip);
+            }
+
+            _c4dbgpf("rem=[{}]~~~{}~~~", rem.len, rem);
+            if(!rem.begins_with('#') && (rem.ends_with(':') || rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t"))))
+            {
+                _c4dbgp("actually, the scalar is the first key of a map, and it opens a new scope");
+                if(m_key_anchor.empty())
+                    _move_val_anchor_to_key_anchor();
+                if(m_key_tag.empty())
+                    _move_val_tag_to_key_tag();
+                addrem_flags(RNXT, RVAL); // before _push_level! This prepares the current level for popping by setting it to RNXT
+                _push_level();
+                _start_map();
+                _store_scalar(s, is_quoted);
+                if( ! _maybe_set_indentation_from_anchor_or_tag())
+                {
+                    _c4dbgpf("set indentation from scalar: {}", m_state->scalar_col);
+                    _set_indentation(m_state->scalar_col); // this is the column where the scalar starts
+                }
+                _move_key_tag2_to_key_tag();
+                addrem_flags(RVAL, RKEY);
+                _line_progressed(1);
+            }
+            else
+            {
+                _c4dbgp("appending val to current seq");
+                _append_val(s, is_quoted);
+                addrem_flags(RNXT, RVAL);
+            }
+            return true;
+        }
+        else if(rem.begins_with("- ") _RYML_WITH_TAB_TOKENS( || rem.begins_with("-\t")))
+        {
+            if(_rval_dash_start_or_continue_seq())
+                _line_progressed(2);
+            return true;
+        }
+        else if(rem == '-')
+        {
+            if(_rval_dash_start_or_continue_seq())
+                _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('['))
+        {
+            _c4dbgp("val is a child seq, flow");
+            addrem_flags(RNXT, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _start_seq();
+            add_flags(FLOW);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('{'))
+        {
+            _c4dbgp("val is a child map, flow");
+            addrem_flags(RNXT, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _start_map();
+            addrem_flags(FLOW|RKEY, RVAL);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with("? "))
+        {
+            _c4dbgp("val is a child map + this key is complex");
+            addrem_flags(RNXT, RVAL); // before _push_level!
+            _push_level();
+            _start_map();
+            addrem_flags(QMRK|RKEY, RVAL);
+            _save_indentation();
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem.begins_with(' '))
+        {
+            csubstr spc = rem.left_of(rem.first_not_of(' '));
+            if(_at_line_begin())
+            {
+                _c4dbgpf("skipping value indentation: {} spaces", spc.len);
+                _line_progressed(spc.len);
+                return true;
+            }
+            else
+            {
+                _c4dbgpf("skipping {} spaces", spc.len);
+                _line_progressed(spc.len);
+                return true;
+            }
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_val_anchors_and_refs())
+        {
+            return true;
+        }
+        /* pathological case:
+         * - &key : val
+         * - &key :
+         * - : val
+         */
+        else if((!has_all(SSCL)) &&
+                (rem.begins_with(": ") || rem.left_of(rem.find("#")).trimr("\t") == ":"))
+        {
+            if(!m_val_anchor.empty() || !m_val_tag.empty())
+            {
+                _c4dbgp("val is a child map + this key is empty, with anchors or tags");
+                addrem_flags(RNXT, RVAL); // before _push_level!
+                _move_val_tag_to_key_tag();
+                _move_val_anchor_to_key_anchor();
+                _push_level();
+                _start_map();
+                _store_scalar_null(rem.str);
+                addrem_flags(RVAL, RKEY);
+                RYML_CHECK(_maybe_set_indentation_from_anchor_or_tag()); // one of them must exist
+                _line_progressed(rem.begins_with(": ") ? 2u : 1u);
+                return true;
+            }
+            else
+            {
+                _c4dbgp("val is a child map + this key is empty, no anchors or tags");
+                addrem_flags(RNXT, RVAL); // before _push_level!
+                size_t ind = m_state->indref;
+                _push_level();
+                _start_map();
+                _store_scalar_null(rem.str);
+                addrem_flags(RVAL, RKEY);
+                _c4dbgpf("set indentation from map anchor: {}", ind + 2);
+                _set_indentation(ind + 2); // this is the column where the map starts
+                _line_progressed(rem.begins_with(": ") ? 2u : 1u);
+                return true;
+            }
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+
+    return false;
+}
+
+//-----------------------------------------------------------------------------
+
+bool Parser::_rval_dash_start_or_continue_seq()
+{
+    size_t ind = m_state->line_contents.current_col();
+    _RYML_CB_ASSERT(m_stack.m_callbacks, ind >= m_state->indref);
+    size_t delta_ind = ind - m_state->indref;
+    if( ! delta_ind)
+    {
+        _c4dbgp("prev val was empty");
+        addrem_flags(RNXT, RVAL);
+        _append_val_null(&m_state->line_contents.full[ind]);
+        return false;
+    }
+    _c4dbgp("val is a nested seq, indented");
+    addrem_flags(RNXT, RVAL); // before _push_level!
+    _push_level();
+    _start_seq();
+    _save_indentation();
+    return true;
+}
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_map_flow()
+{
+    // explicit flow, ie, inside {}, separated by commas
+    _c4dbgpf("handle_map_flow: node_id={}  level={}", m_state->node_id, m_state->level);
+    csubstr rem = m_state->line_contents.rem;
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RMAP|FLOW));
+
+    if(rem.begins_with(' '))
+    {
+        // with explicit flow, indentation does not matter
+        _c4dbgp("starts with spaces");
+        _skipchars(' ');
+        return true;
+    }
+    _RYML_WITH_TAB_TOKENS(else if(rem.begins_with('\t'))
+    {
+        // with explicit flow, indentation does not matter
+        _c4dbgp("starts with tabs");
+        _skipchars('\t');
+        return true;
+    })
+    else if(rem.begins_with('#'))
+    {
+        _c4dbgp("it's a comment");
+        rem = _scan_comment(); // also progresses the line
+        return true;
+    }
+    else if(rem.begins_with('}'))
+    {
+        _c4dbgp("end the map");
+        if(has_all(SSCL))
+        {
+            _c4dbgp("the last val was null");
+            _append_key_val_null(rem.str - 1);
+            rem_flags(RVAL);
+        }
+        _pop_level();
+        _line_progressed(1);
+        if(has_all(RSEQIMAP))
+        {
+            _c4dbgp("stopping implicitly nested 1x map");
+            _stop_seqimap();
+            _pop_level();
+        }
+        return true;
+    }
+
+    if(has_any(RNXT))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RSEQIMAP));
+
+        if(rem.begins_with(", "))
+        {
+            _c4dbgp("seq: expect next keyval");
+            addrem_flags(RKEY, RNXT);
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem.begins_with(','))
+        {
+            _c4dbgp("seq: expect next keyval");
+            addrem_flags(RKEY, RNXT);
+            _line_progressed(1);
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else if(has_any(RKEY))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+
+        bool is_quoted;
+        if(has_none(SSCL) && _scan_scalar_map_flow(&rem, &is_quoted))
+        {
+            _c4dbgp("it's a scalar");
+            _store_scalar(rem, is_quoted);
+            rem = m_state->line_contents.rem;
+            csubstr trimmed = rem.triml(" \t");
+            if(trimmed.len && (trimmed.begins_with(": ") || trimmed.begins_with_any(":,}") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t"))))
+            {
+                _RYML_CB_ASSERT(m_stack.m_callbacks, trimmed.str >= rem.str);
+                size_t num = static_cast<size_t>(trimmed.str - rem.str);
+                _c4dbgpf("trimming {} whitespace after the scalar: '{}' --> '{}'", num, rem, rem.sub(num));
+                rem = rem.sub(num);
+                _line_progressed(num);
+            }
+        }
+
+        if(rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+        {
+            _c4dbgp("wait for val");
+            addrem_flags(RVAL, RKEY|QMRK);
+            _line_progressed(2);
+            if(!has_all(SSCL))
+            {
+                _c4dbgp("no key was found, defaulting to empty key ''");
+                _store_scalar_null(rem.str);
+            }
+            return true;
+        }
+        else if(rem == ':')
+        {
+            _c4dbgp("wait for val");
+            addrem_flags(RVAL, RKEY|QMRK);
+            _line_progressed(1);
+            if(!has_all(SSCL))
+            {
+                _c4dbgp("no key was found, defaulting to empty key ''");
+                _store_scalar_null(rem.str);
+            }
+            return true;
+        }
+        else if(rem.begins_with('?'))
+        {
+            _c4dbgp("complex key");
+            add_flags(QMRK);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with(','))
+        {
+            _c4dbgp("prev scalar was a key with null value");
+            _append_key_val_null(rem.str - 1);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('}'))
+        {
+            _c4dbgp("map terminates after a key...");
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(SSCL));
+            _c4dbgp("the last val was null");
+            _append_key_val_null(rem.str - 1);
+            rem_flags(RVAL);
+            if(has_all(RSEQIMAP))
+            {
+                _c4dbgp("stopping implicitly nested 1x map");
+                _stop_seqimap();
+                _pop_level();
+            }
+            _pop_level();
+            _line_progressed(1);
+            return true;
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_key_anchors_and_refs())
+        {
+            return true;
+        }
+        else if(rem == "")
+        {
+            return true;
+        }
+        else
+        {
+            size_t pos = rem.first_not_of(" \t");
+            if(pos == csubstr::npos)
+               pos = 0;
+            rem = rem.sub(pos);
+            if(rem.begins_with(':'))
+            {
+                _c4dbgp("wait for val");
+                addrem_flags(RVAL, RKEY|QMRK);
+                _line_progressed(pos + 1);
+                if(!has_all(SSCL))
+                {
+                    _c4dbgp("no key was found, defaulting to empty key ''");
+                    _store_scalar_null(rem.str);
+                }
+                return true;
+            }
+            else if(rem.begins_with('#'))
+            {
+                _c4dbgp("it's a comment");
+                _line_progressed(pos);
+                rem = _scan_comment(); // also progresses the line
+                return true;
+            }
+            else
+            {
+                _c4err("parse error");
+            }
+        }
+    }
+    else if(has_any(RVAL))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(SSCL));
+        bool is_quoted;
+        if(_scan_scalar_map_flow(&rem, &is_quoted))
+        {
+            _c4dbgp("it's a scalar");
+            addrem_flags(RNXT, RVAL|RKEY);
+            _append_key_val(rem, is_quoted);
+            if(has_all(RSEQIMAP))
+            {
+                _c4dbgp("stopping implicitly nested 1x map");
+                _stop_seqimap();
+                _pop_level();
+            }
+            return true;
+        }
+        else if(rem.begins_with('['))
+        {
+            _c4dbgp("val is a child seq");
+            addrem_flags(RNXT, RVAL|RKEY); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _move_scalar_from_top();
+            _start_seq();
+            add_flags(FLOW);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('{'))
+        {
+            _c4dbgp("val is a child map");
+            addrem_flags(RNXT, RVAL|RKEY); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _move_scalar_from_top();
+            _start_map();
+            addrem_flags(FLOW|RKEY, RNXT|RVAL);
+            _line_progressed(1);
+            return true;
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_val_anchors_and_refs())
+        {
+            return true;
+        }
+        else if(rem.begins_with(','))
+        {
+            _c4dbgp("appending empty val");
+            _append_key_val_null(rem.str - 1);
+            addrem_flags(RKEY, RVAL);
+            _line_progressed(1);
+            if(has_any(RSEQIMAP))
+            {
+                _c4dbgp("stopping implicitly nested 1x map");
+                _stop_seqimap();
+                _pop_level();
+            }
+            return true;
+        }
+        else if(has_any(RSEQIMAP) && rem.begins_with(']'))
+        {
+            _c4dbgp("stopping implicitly nested 1x map");
+            if(has_any(SSCL))
+            {
+                _append_key_val_null(rem.str - 1);
+            }
+            _stop_seqimap();
+            _pop_level();
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else
+    {
+        _c4err("internal error");
+    }
+
+    return false;
+}
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_map_blck()
+{
+    _c4dbgpf("handle_map_blck: node_id={}  level={}", m_state->node_id, m_state->level);
+    csubstr rem = m_state->line_contents.rem;
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RMAP));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(FLOW));
+
+    if(rem.begins_with('#'))
+    {
+        _c4dbgp("it's a comment");
+        rem = _scan_comment();
+        return true;
+    }
+
+    if(has_any(RNXT))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+        // actually, we don't need RNXT in indent-based maps.
+        addrem_flags(RKEY, RNXT);
+    }
+
+    if(_handle_indentation())
+    {
+        _c4dbgp("indentation token");
+        return true;
+    }
+
+    if(has_any(RKEY))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RVAL));
+
+        _c4dbgp("RMAP|RKEY read scalar?");
+        bool is_quoted;
+        if(_scan_scalar_map_blck(&rem, &is_quoted)) // this also progresses the line
+        {
+            _c4dbgpf("it's a{} scalar", is_quoted ? " quoted" : "");
+            if(has_all(QMRK|SSCL))
+            {
+                _c4dbgpf("current key is QMRK; SSCL is set. so take store scalar='{}' as key and add an empty val", m_state->scalar);
+                _append_key_val_null(rem.str - 1);
+            }
+            _store_scalar(rem, is_quoted);
+            if(has_all(QMRK|RSET))
+            {
+                _c4dbgp("it's a complex key, so use null value '~'");
+                _append_key_val_null(rem.str);
+            }
+            rem = m_state->line_contents.rem;
+
+            if(rem.begins_with(':'))
+            {
+                _c4dbgp("wait for val");
+                addrem_flags(RVAL, RKEY|QMRK);
+                _line_progressed(1);
+                rem = m_state->line_contents.rem;
+                if(rem.begins_with_any(" \t"))
+                {
+                    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! _at_line_begin());
+                    rem = rem.left_of(rem.first_not_of(" \t"));
+                    _c4dbgpf("skip {} spaces/tabs", rem.len);
+                    _line_progressed(rem.len);
+                }
+            }
+            return true;
+        }
+        else if(rem.begins_with_any(" \t"))
+        {
+            size_t pos = rem.first_not_of(" \t");
+            if(pos == npos)
+                pos = rem.len;
+            _c4dbgpf("skip {} spaces/tabs", pos);
+            _line_progressed(pos);
+            return true;
+        }
+        else if(rem == '?' || rem.begins_with("? "))
+        {
+            _c4dbgp("it's a complex key");
+            _line_progressed(rem.begins_with("? ") ? 2u : 1u);
+            if(has_any(SSCL))
+                _append_key_val_null(rem.str - 1);
+            add_flags(QMRK);
+            return true;
+        }
+        else if(has_all(QMRK) && rem.begins_with(':'))
+        {
+            _c4dbgp("complex key finished");
+            if(!has_any(SSCL))
+                _store_scalar_null(rem.str);
+            addrem_flags(RVAL, RKEY|QMRK);
+            _line_progressed(1);
+            rem = m_state->line_contents.rem;
+            if(rem.begins_with(' '))
+            {
+                _RYML_CB_ASSERT(m_stack.m_callbacks,  ! _at_line_begin());
+                _skipchars(' ');
+            }
+            return true;
+        }
+        else if(rem == ':' || rem.begins_with(": ") _RYML_WITH_TAB_TOKENS( || rem.begins_with(":\t")))
+        {
+            _c4dbgp("key finished");
+            if(!has_all(SSCL))
+            {
+                _c4dbgp("key was empty...");
+                _store_scalar_null(rem.str);
+                rem_flags(QMRK);
+            }
+            addrem_flags(RVAL, RKEY);
+            _line_progressed(rem == ':' ? 1 : 2);
+            return true;
+        }
+        else if(rem.begins_with("..."))
+        {
+            _c4dbgp("end current document");
+            _end_stream();
+            _line_progressed(3);
+            return true;
+        }
+        else if(rem.begins_with("---"))
+        {
+            _c4dbgp("start new document '---'");
+            _start_new_doc(rem);
+            return true;
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_key_anchors_and_refs())
+        {
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else if(has_any(RVAL))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RNXT));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RKEY));
+
+        _c4dbgp("RMAP|RVAL read scalar?");
+        csubstr s;
+        bool is_quoted;
+        if(_scan_scalar_map_blck(&s, &is_quoted)) // this also progresses the line
+        {
+            _c4dbgpf("it's a{} scalar", is_quoted ? " quoted" : "");
+
+            rem = m_state->line_contents.rem;
+
+            if(rem.begins_with(": "))
+            {
+                _c4dbgp("actually, the scalar is the first key of a map");
+                addrem_flags(RKEY, RVAL); // before _push_level! This prepares the current level for popping by setting it to RNXT
+                _push_level();
+                _move_scalar_from_top();
+                _move_val_anchor_to_key_anchor();
+                _start_map();
+                _save_indentation(m_state->scalar_col);
+                addrem_flags(RVAL, RKEY);
+                _line_progressed(2);
+            }
+            else if(rem.begins_with(':'))
+            {
+                _c4dbgp("actually, the scalar is the first key of a map, and it opens a new scope");
+                addrem_flags(RKEY, RVAL); // before _push_level! This prepares the current level for popping by setting it to RNXT
+                _push_level();
+                _move_scalar_from_top();
+                _move_val_anchor_to_key_anchor();
+                _start_map();
+                _save_indentation(/*behind*/s.len);
+                addrem_flags(RVAL, RKEY);
+                _line_progressed(1);
+            }
+            else
+            {
+                _c4dbgp("appending keyval to current map");
+                _append_key_val(s, is_quoted);
+                addrem_flags(RKEY, RVAL);
+            }
+            return true;
+        }
+        else if(rem.begins_with("- ") _RYML_WITH_TAB_TOKENS( || rem.begins_with("-\t")))
+        {
+            _c4dbgp("val is a nested seq, indented");
+            addrem_flags(RKEY, RVAL); // before _push_level!
+            _push_level();
+            _move_scalar_from_top();
+            _start_seq();
+            _save_indentation();
+            _line_progressed(2);
+            return true;
+        }
+        else if(rem == '-')
+        {
+            _c4dbgp("maybe a seq. start unknown, indented");
+            _start_unk();
+            _save_indentation();
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('['))
+        {
+            _c4dbgp("val is a child seq, flow");
+            addrem_flags(RKEY, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _move_scalar_from_top();
+            _start_seq();
+            add_flags(FLOW);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with('{'))
+        {
+            _c4dbgp("val is a child map, flow");
+            addrem_flags(RKEY, RVAL); // before _push_level!
+            _push_level(/*explicit flow*/true);
+            _move_scalar_from_top();
+            _start_map();
+            addrem_flags(FLOW|RKEY, RVAL);
+            _line_progressed(1);
+            return true;
+        }
+        else if(rem.begins_with(' '))
+        {
+            csubstr spc = rem.left_of(rem.first_not_of(' '));
+            if(_at_line_begin())
+            {
+                _c4dbgpf("skipping value indentation: {} spaces", spc.len);
+                _line_progressed(spc.len);
+                return true;
+            }
+            else
+            {
+                _c4dbgpf("skipping {} spaces", spc.len);
+                _line_progressed(spc.len);
+                return true;
+            }
+        }
+        else if(_handle_types())
+        {
+            return true;
+        }
+        else if(_handle_val_anchors_and_refs())
+        {
+            return true;
+        }
+        else if(rem.begins_with("--- ") || rem == "---" || rem.begins_with("---\t"))
+        {
+            _start_new_doc(rem);
+            return true;
+        }
+        else if(rem.begins_with("..."))
+        {
+            _c4dbgp("end current document");
+            _end_stream();
+            _line_progressed(3);
+            return true;
+        }
+        else
+        {
+            _c4err("parse error");
+        }
+    }
+    else
+    {
+        _c4err("internal error");
+    }
+
+    return false;
+}
+
+
+//-----------------------------------------------------------------------------
+bool Parser::_handle_top()
+{
+    _c4dbgp("handle_top");
+    csubstr rem = m_state->line_contents.rem;
+
+    if(rem.begins_with('#'))
+    {
+        _c4dbgp("a comment line");
+        _scan_comment();
+        return true;
+    }
+
+    csubstr trimmed = rem.triml(' ');
+
+    if(trimmed.begins_with('%'))
+    {
+        _handle_directive(trimmed);
+        _line_progressed(rem.len);
+        return true;
+    }
+    else if(trimmed.begins_with("--- ") || trimmed == "---" || trimmed.begins_with("---\t"))
+    {
+        _start_new_doc(rem);
+        if(trimmed.len < rem.len)
+        {
+            _line_progressed(rem.len - trimmed.len);
+            _save_indentation();
+        }
+        return true;
+    }
+    else if(trimmed.begins_with("..."))
+    {
+        _c4dbgp("end current document");
+        _end_stream();
+        if(trimmed.len < rem.len)
+        {
+            _line_progressed(rem.len - trimmed.len);
+        }
+        _line_progressed(3);
+        return true;
+    }
+    else
+    {
+        _c4err("parse error");
+    }
+
+    return false;
+}
+
+
+//-----------------------------------------------------------------------------
+
+bool Parser::_handle_key_anchors_and_refs()
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, !has_any(RVAL));
+    const csubstr rem = m_state->line_contents.rem;
+    if(rem.begins_with('&'))
+    {
+        _c4dbgp("found a key anchor!!!");
+        if(has_all(QMRK|SSCL))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_any(RKEY));
+            _c4dbgp("there is a stored key, so this anchor is for the next element");
+            _append_key_val_null(rem.str - 1);
+            rem_flags(QMRK);
+            return true;
+        }
+        csubstr anchor = rem.left_of(rem.first_of(' '));
+        _line_progressed(anchor.len);
+        anchor = anchor.sub(1); // skip the first character
+        _move_key_anchor_to_val_anchor();
+        _c4dbgpf("key anchor value: '{}'", anchor);
+        m_key_anchor = anchor;
+        m_key_anchor_indentation = m_state->line_contents.current_col(rem);
+        return true;
+    }
+    else if(C4_UNLIKELY(rem.begins_with('*')))
+    {
+        _c4err("not implemented - this should have been catched elsewhere");
+        C4_NEVER_REACH();
+        return false;
+    }
+    return false;
+}
+
+bool Parser::_handle_val_anchors_and_refs()
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, !has_any(RKEY));
+    const csubstr rem = m_state->line_contents.rem;
+    if(rem.begins_with('&'))
+    {
+        csubstr anchor = rem.left_of(rem.first_of(' '));
+        _line_progressed(anchor.len);
+        anchor = anchor.sub(1); // skip the first character
+        _c4dbgpf("val: found an anchor: '{}', indentation={}!!!", anchor, m_state->line_contents.current_col(rem));
+        if(m_val_anchor.empty())
+        {
+            _c4dbgpf("save val anchor: '{}'", anchor);
+            m_val_anchor = anchor;
+            m_val_anchor_indentation = m_state->line_contents.current_col(rem);
+        }
+        else
+        {
+            _c4dbgpf("there is a pending val anchor '{}'", m_val_anchor);
+            if(m_tree->is_seq(m_state->node_id))
+            {
+                if(m_tree->has_children(m_state->node_id))
+                {
+                    _c4dbgpf("current node={} is a seq, has {} children", m_state->node_id, m_tree->num_children(m_state->node_id));
+                    _c4dbgpf("... so take the new one as a key anchor '{}'", anchor);
+                    m_key_anchor = anchor;
+                    m_key_anchor_indentation = m_state->line_contents.current_col(rem);
+                }
+                else
+                {
+                    _c4dbgpf("current node={} is a seq, has no children", m_state->node_id);
+                    if(m_tree->has_val_anchor(m_state->node_id))
+                    {
+                        _c4dbgpf("... node={} already has val anchor: '{}'", m_state->node_id, m_tree->val_anchor(m_state->node_id));
+                        _c4dbgpf("... so take the new one as a key anchor '{}'", anchor);
+                        m_key_anchor = anchor;
+                        m_key_anchor_indentation = m_state->line_contents.current_col(rem);
+                    }
+                    else
+                    {
+                        _c4dbgpf("... so set pending val anchor: '{}' on current node {}", m_val_anchor, m_state->node_id);
+                        m_tree->set_val_anchor(m_state->node_id, m_val_anchor);
+                        m_val_anchor = anchor;
+                        m_val_anchor_indentation = m_state->line_contents.current_col(rem);
+                    }
+                }
+            }
+        }
+        return true;
+    }
+    else if(C4_UNLIKELY(rem.begins_with('*')))
+    {
+        _c4err("not implemented - this should have been catched elsewhere");
+        C4_NEVER_REACH();
+        return false;
+    }
+    return false;
+}
+
+void Parser::_move_key_anchor_to_val_anchor()
+{
+    if(m_key_anchor.empty())
+        return;
+    _c4dbgpf("move current key anchor to val slot: key='{}' -> val='{}'", m_key_anchor, m_val_anchor);
+    if(!m_val_anchor.empty())
+        _c4err("triple-pending anchor");
+    m_val_anchor = m_key_anchor;
+    m_val_anchor_indentation = m_key_anchor_indentation;
+    m_key_anchor = {};
+    m_key_anchor_indentation = {};
+}
+
+void Parser::_move_val_anchor_to_key_anchor()
+{
+    if(m_val_anchor.empty())
+        return;
+    if(!_token_is_from_this_line(m_val_anchor))
+        return;
+    _c4dbgpf("move current val anchor to key slot: key='{}' <- val='{}'", m_key_anchor, m_val_anchor);
+    if(!m_key_anchor.empty())
+        _c4err("triple-pending anchor");
+    m_key_anchor = m_val_anchor;
+    m_key_anchor_indentation = m_val_anchor_indentation;
+    m_val_anchor = {};
+    m_val_anchor_indentation = {};
+}
+
+void Parser::_move_key_tag_to_val_tag()
+{
+    if(m_key_tag.empty())
+        return;
+    _c4dbgpf("move key tag to val tag: key='{}' -> val='{}'", m_key_tag, m_val_tag);
+    m_val_tag = m_key_tag;
+    m_val_tag_indentation = m_key_tag_indentation;
+    m_key_tag.clear();
+    m_key_tag_indentation = 0;
+}
+
+void Parser::_move_val_tag_to_key_tag()
+{
+    if(m_val_tag.empty())
+        return;
+    if(!_token_is_from_this_line(m_val_tag))
+        return;
+    _c4dbgpf("move val tag to key tag: key='{}' <- val='{}'", m_key_tag, m_val_tag);
+    m_key_tag = m_val_tag;
+    m_key_tag_indentation = m_val_tag_indentation;
+    m_val_tag.clear();
+    m_val_tag_indentation = 0;
+}
+
+void Parser::_move_key_tag2_to_key_tag()
+{
+    if(m_key_tag2.empty())
+        return;
+    _c4dbgpf("move key tag2 to key tag: key='{}' <- key2='{}'", m_key_tag, m_key_tag2);
+    m_key_tag = m_key_tag2;
+    m_key_tag_indentation = m_key_tag2_indentation;
+    m_key_tag2.clear();
+    m_key_tag2_indentation = 0;
+}
+
+
+//-----------------------------------------------------------------------------
+
+bool Parser::_handle_types()
+{
+    csubstr rem = m_state->line_contents.rem.triml(' ');
+    csubstr t;
+
+    if(rem.begins_with("!!"))
+    {
+        _c4dbgp("begins with '!!'");
+        t = rem.left_of(rem.first_of(" ,"));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, t.len >= 2);
+        //t = t.sub(2);
+        if(t == "!!set")
+            add_flags(RSET);
+    }
+    else if(rem.begins_with("!<"))
+    {
+        _c4dbgp("begins with '!<'");
+        t = rem.left_of(rem.first_of('>'), true);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, t.len >= 2);
+        //t = t.sub(2, t.len-1);
+    }
+    else if(rem.begins_with("!h!"))
+    {
+        _c4dbgp("begins with '!h!'");
+        t = rem.left_of(rem.first_of(' '));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, t.len >= 3);
+        //t = t.sub(3);
+    }
+    else if(rem.begins_with('!'))
+    {
+        _c4dbgp("begins with '!'");
+        t = rem.left_of(rem.first_of(' '));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, t.len >= 1);
+        //t = t.sub(1);
+    }
+
+    if(t.empty())
+        return false;
+
+    if(has_all(QMRK|SSCL))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_any(RKEY));
+        _c4dbgp("there is a stored key, so this tag is for the next element");
+        _append_key_val_null(rem.str - 1);
+        rem_flags(QMRK);
+    }
+
+    #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+    const char *tag_beginning = rem.str;
+    #endif
+    size_t tag_indentation = m_state->line_contents.current_col(t);
+    _c4dbgpf("there was a tag: '{}', indentation={}", t, tag_indentation);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, t.end() > m_state->line_contents.rem.begin());
+    _line_progressed(static_cast<size_t>(t.end() - m_state->line_contents.rem.begin()));
+    {
+        size_t pos = m_state->line_contents.rem.first_not_of(" \t");
+        if(pos != csubstr::npos)
+            _line_progressed(pos);
+    }
+
+    if(has_all(RMAP|RKEY))
+    {
+        _c4dbgpf("saving map key tag '{}'", t);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_key_tag.empty());
+        m_key_tag = t;
+        m_key_tag_indentation = tag_indentation;
+    }
+    else if(has_all(RMAP|RVAL))
+    {
+        /* foo: !!str
+         * !!str : bar  */
+        rem = m_state->line_contents.rem;
+        rem = rem.left_of(rem.find("#"));
+        rem = rem.trimr(" \t");
+        _c4dbgpf("rem='{}'", rem);
+        #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+        if(rem == ':' || rem.begins_with(": "))
+        {
+            _c4dbgp("the last val was null, and this is a tag from a null key");
+            _append_key_val_null(tag_beginning - 1);
+            _store_scalar_null(rem.str - 1);
+            // do not change the flag to key, it is ~
+            _RYML_CB_ASSERT(m_stack.m_callbacks, rem.begin() > m_state->line_contents.rem.begin());
+            size_t token_len = rem == ':' ? 1 : 2;
+            _line_progressed(static_cast<size_t>(token_len + rem.begin() - m_state->line_contents.rem.begin()));
+        }
+        #endif
+        _c4dbgpf("saving map val tag '{}'", t);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_val_tag.empty());
+        m_val_tag = t;
+        m_val_tag_indentation = tag_indentation;
+    }
+    else if(has_all(RSEQ|RVAL) || has_all(RTOP|RUNK|NDOC))
+    {
+        if(m_val_tag.empty())
+        {
+            _c4dbgpf("saving seq/doc val tag '{}'", t);
+            m_val_tag = t;
+            m_val_tag_indentation = tag_indentation;
+        }
+        else
+        {
+            _c4dbgpf("saving seq/doc key tag '{}'", t);
+            m_key_tag = t;
+            m_key_tag_indentation = tag_indentation;
+        }
+    }
+    else if(has_all(RTOP|RUNK) || has_any(RUNK))
+    {
+        rem = m_state->line_contents.rem;
+        rem = rem.left_of(rem.find("#"));
+        rem = rem.trimr(" \t");
+        if(rem.empty())
+        {
+            _c4dbgpf("saving val tag '{}'", t);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_val_tag.empty());
+            m_val_tag = t;
+            m_val_tag_indentation = tag_indentation;
+        }
+        else
+        {
+            _c4dbgpf("saving key tag '{}'", t);
+            if(m_key_tag.empty())
+            {
+                m_key_tag = t;
+                m_key_tag_indentation = tag_indentation;
+            }
+            else
+            {
+                /* handle this case:
+                 * !!str foo: !!map
+                 *   !!int 1: !!float 20.0
+                 *   !!int 3: !!float 40.0
+                 *
+                 * (m_key_tag would be !!str and m_key_tag2 would be !!int)
+                 */
+                m_key_tag2 = t;
+                m_key_tag2_indentation = tag_indentation;
+            }
+        }
+    }
+    else
+    {
+        _c4err("internal error");
+    }
+
+    if(m_val_tag.not_empty())
+    {
+        YamlTag_e tag = to_tag(t);
+        if(tag == TAG_STR)
+        {
+            _c4dbgpf("tag '{}' is a str-type tag", t);
+            if(has_all(RTOP|RUNK|NDOC))
+            {
+                _c4dbgpf("docval. slurping the string. pos={}", m_state->pos.offset);
+                csubstr scalar = _slurp_doc_scalar();
+                _c4dbgpf("docval. after slurp: {}, at node {}: '{}'", m_state->pos.offset, m_state->node_id, scalar);
+                m_tree->to_val(m_state->node_id, scalar, DOC);
+                _c4dbgpf("docval. val tag {} -> {}", m_val_tag, normalize_tag(m_val_tag));
+                m_tree->set_val_tag(m_state->node_id, normalize_tag(m_val_tag));
+                m_val_tag.clear();
+                if(!m_val_anchor.empty())
+                {
+                    _c4dbgpf("setting val anchor[{}]='{}'", m_state->node_id, m_val_anchor);
+                    m_tree->set_val_anchor(m_state->node_id, m_val_anchor);
+                    m_val_anchor.clear();
+                }
+                _end_stream();
+            }
+        }
+    }
+    return true;
+}
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_slurp_doc_scalar()
+{
+    csubstr s = m_state->line_contents.rem;
+    size_t pos = m_state->pos.offset;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.full.find("---") != csubstr::npos);
+    _c4dbgpf("slurp 0 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+    if(s.len == 0)
+    {
+        _line_ended();
+        _scan_line();
+        s = m_state->line_contents.rem;
+        pos = m_state->pos.offset;
+    }
+
+    size_t skipws = s.first_not_of(" \t");
+    _c4dbgpf("slurp 1 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+    if(skipws != npos)
+    {
+        _line_progressed(skipws);
+        s = m_state->line_contents.rem;
+        pos = m_state->pos.offset;
+        _c4dbgpf("slurp 2 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_val_anchor.empty());
+    _handle_val_anchors_and_refs();
+    if(!m_val_anchor.empty())
+    {
+        s = m_state->line_contents.rem;
+        skipws = s.first_not_of(" \t");
+        if(skipws != npos)
+        {
+            _line_progressed(skipws);
+        }
+        s = m_state->line_contents.rem;
+        pos = m_state->pos.offset;
+        _c4dbgpf("slurp 3 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+    }
+
+    if(s.begins_with('\''))
+    {
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        return _scan_squot_scalar();
+    }
+    else if(s.begins_with('"'))
+    {
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        return _scan_dquot_scalar();
+    }
+    else if(s.begins_with('|') || s.begins_with('>'))
+    {
+        return _scan_block();
+    }
+
+    _c4dbgpf("slurp 4 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.end() >= m_buf.begin() + pos);
+    _line_progressed(static_cast<size_t>(s.end() - (m_buf.begin() + pos)));
+
+    _c4dbgpf("slurp 5 '{}'. REM='{}'", s, m_buf.sub(m_state->pos.offset));
+
+    if(_at_line_end())
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    return s;
+}
+
+
+//-----------------------------------------------------------------------------
+
+bool Parser::_scan_scalar_seq_blck(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RSEQ));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RVAL));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(RKEY));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(FLOW));
+
+    csubstr s = m_state->line_contents.rem;
+    if(s.len == 0)
+        return false;
+    s = s.trim(" \t");
+    if(s.len == 0)
+        return false;
+
+    if(s.begins_with('\''))
+    {
+        _c4dbgp("got a ': scanning single-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_squot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('"'))
+    {
+        _c4dbgp("got a \": scanning double-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_dquot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('|') || s.begins_with('>'))
+    {
+        *scalar = _scan_block();
+        *quoted = true;
+        return true;
+    }
+    else if(has_any(RTOP) && _is_doc_sep(s))
+    {
+        return false;
+    }
+
+    _c4dbgp("RSEQ|RVAL");
+    if( ! _is_scalar_next__rseq_rval(s))
+        return false;
+    _RYML_WITH_TAB_TOKENS(else if(s.begins_with("-\t"))
+        return false;
+    )
+
+    if(s.ends_with(':'))
+    {
+        --s.len;
+    }
+    else
+    {
+        auto first = s.first_of_any(": " _RYML_WITH_TAB_TOKENS( , ":\t"), " #");
+        if(first)
+            s.len = first.pos;
+    }
+    s = s.trimr(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+
+    if(s.empty())
+        return false;
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.str >= m_state->line_contents.rem.str);
+    _line_progressed(static_cast<size_t>(s.str - m_state->line_contents.rem.str) + s.len);
+
+    if(_at_line_end() && s != '~')
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    *scalar = s;
+    *quoted = false;
+    return true;
+}
+
+bool Parser::_scan_scalar_map_blck(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted)
+{
+    _c4dbgp("_scan_scalar_map_blck");
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RMAP));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(FLOW));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RKEY|RVAL));
+
+    csubstr s = m_state->line_contents.rem;
+    #ifdef RYML_NO_COVERAGE__TO_BE_DELETED__OR_REFACTORED
+    if(s.len == 0)
+        return false;
+    #endif
+    s = s.trim(" \t");
+    if(s.len == 0)
+        return false;
+
+    if(s.begins_with('\''))
+    {
+        _c4dbgp("got a ': scanning single-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_squot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('"'))
+    {
+        _c4dbgp("got a \": scanning double-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_dquot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('|') || s.begins_with('>'))
+    {
+        *scalar = _scan_block();
+        *quoted = true;
+        return true;
+    }
+    else if(has_any(RTOP) && _is_doc_sep(s))
+    {
+        return false;
+    }
+
+    if( ! _is_scalar_next__rmap(s))
+        return false;
+
+    size_t colon_token = s.find(": ");
+    if(colon_token == npos)
+    {
+        _RYML_WITH_OR_WITHOUT_TAB_TOKENS(
+            // with tab tokens
+            colon_token = s.find(":\t");
+            if(colon_token == npos)
+            {
+                _RYML_CB_ASSERT(m_stack.m_callbacks, s.len > 0);
+                colon_token = s.find(':');
+                if(colon_token != s.len-1)
+                    colon_token = npos;
+            }
+            ,
+            // without tab tokens
+            colon_token = s.find(':');
+            _RYML_CB_ASSERT(m_stack.m_callbacks, s.len > 0);
+            if(colon_token != s.len-1)
+                colon_token = npos;
+        )
+    }
+
+    if(has_all(RKEY))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, !s.begins_with(' '));
+        if(has_any(QMRK))
+        {
+            _c4dbgp("RMAP|RKEY|CPLX");
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_any(RMAP));
+            if(s.begins_with("? ") || s == '?')
+                return false;
+            s = s.left_of(colon_token);
+            s = s.left_of(s.first_of("#"));
+            s = s.trimr(" \t");
+            if(s.begins_with("---"))
+                return false;
+            else if(s.begins_with("..."))
+                return false;
+        }
+        else
+        {
+            _c4dbgp("RMAP|RKEY");
+            _RYML_CB_CHECK(m_stack.m_callbacks, !s.begins_with('{'));
+            if(s.begins_with("? ") || s == '?')
+                return false;
+            s = s.left_of(colon_token);
+            s = s.trimr(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+            if(s.begins_with("---"))
+            {
+                return false;
+            }
+            else if(s.begins_with("..."))
+            {
+                return false;
+            }
+        }
+    }
+    else if(has_all(RVAL))
+    {
+        _c4dbgp("RMAP|RVAL");
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(QMRK));
+        if( ! _is_scalar_next__rmap_val(s))
+            return false;
+        _RYML_WITH_TAB_TOKENS(
+        else if(s.begins_with("-\t"))
+            return false;
+        )
+        _c4dbgp("RMAP|RVAL: scalar");
+        s = s.left_of(s.find(" #")); // is there a comment?
+        s = s.left_of(s.find("\t#")); // is there a comment?
+        s = s.trim(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+        if(s.begins_with("---"))
+            return false;
+        #ifdef RYML_NO_COVERAGE__TO_BE_DELETED__OR_REFACTORED
+        else if(s.begins_with("..."))
+            return false;
+        #endif
+    }
+
+    if(s.empty())
+        return false;
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.str >= m_state->line_contents.rem.str);
+    _line_progressed(static_cast<size_t>(s.str - m_state->line_contents.rem.str) + s.len);
+
+    if(_at_line_end() && s != '~')
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    *scalar = s;
+    *quoted = false;
+    return true;
+}
+
+bool Parser::_scan_scalar_seq_flow(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RSEQ));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(FLOW));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RVAL));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(RKEY));
+
+    csubstr s = m_state->line_contents.rem;
+    if(s.len == 0)
+        return false;
+    s = s.trim(" \t");
+    if(s.len == 0)
+        return false;
+
+    if(s.begins_with('\''))
+    {
+        _c4dbgp("got a ': scanning single-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_squot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('"'))
+    {
+        _c4dbgp("got a \": scanning double-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_dquot_scalar();
+        *quoted = true;
+        return true;
+    }
+
+    if(has_all(RVAL))
+    {
+        _c4dbgp("RSEQ|RVAL");
+        if( ! _is_scalar_next__rseq_rval(s))
+            return false;
+        _RYML_WITH_TAB_TOKENS(else if(s.begins_with("-\t"))
+            return false;
+        )
+        _c4dbgp("RSEQ|RVAL|FLOW");
+        s = s.left_of(s.first_of(",]"));
+        if(s.ends_with(':'))
+        {
+            --s.len;
+        }
+        else
+        {
+            auto first = s.first_of_any(": " _RYML_WITH_TAB_TOKENS( , ":\t"), " #");
+            if(first)
+                s.len = first.pos;
+        }
+        s = s.trimr(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+    }
+
+    if(s.empty())
+        return false;
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.str >= m_state->line_contents.rem.str);
+    _line_progressed(static_cast<size_t>(s.str - m_state->line_contents.rem.str) + s.len);
+
+    if(_at_line_end() && s != '~')
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    *scalar = s;
+    *quoted = false;
+    return true;
+}
+
+bool Parser::_scan_scalar_map_flow(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RMAP));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(FLOW));
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RKEY|RVAL));
+
+    csubstr s = m_state->line_contents.rem;
+    if(s.len == 0)
+        return false;
+    s = s.trim(" \t");
+    if(s.len == 0)
+        return false;
+
+    if(s.begins_with('\''))
+    {
+        _c4dbgp("got a ': scanning single-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_squot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('"'))
+    {
+        _c4dbgp("got a \": scanning double-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_dquot_scalar();
+        *quoted = true;
+        return true;
+    }
+
+    if( ! _is_scalar_next__rmap(s))
+        return false;
+
+    if(has_all(RKEY))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, !s.begins_with(' '));
+        size_t colon_token = s.find(": ");
+        if(colon_token == npos)
+        {
+            _RYML_WITH_OR_WITHOUT_TAB_TOKENS(
+                // with tab tokens
+                colon_token = s.find(":\t");
+                if(colon_token == npos)
+                {
+                    _RYML_CB_ASSERT(m_stack.m_callbacks, s.len > 0);
+                    colon_token = s.find(':');
+                    if(colon_token != s.len-1)
+                        colon_token = npos;
+                }
+                ,
+                // without tab tokens
+                colon_token = s.find(':');
+                _RYML_CB_ASSERT(m_stack.m_callbacks, s.len > 0);
+                if(colon_token != s.len-1)
+                    colon_token = npos;
+            )
+        }
+        if(s.begins_with("? ") || s == '?')
+            return false;
+        if(has_any(QMRK))
+        {
+            _c4dbgp("RMAP|RKEY|CPLX");
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_any(RMAP));
+            s = s.left_of(colon_token);
+            s = s.left_of(s.first_of("#"));
+            s = s.left_of(s.first_of(':'));
+            s = s.trimr(" \t");
+            if(s.begins_with("---"))
+                return false;
+            else if(s.begins_with("..."))
+                return false;
+        }
+        else
+        {
+            _RYML_CB_CHECK(m_stack.m_callbacks, !s.begins_with('{'));
+            _c4dbgp("RMAP|RKEY");
+            s = s.left_of(colon_token);
+            s = s.trimr(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+            _c4dbgpf("RMAP|RKEY|FLOW: '{}'", s);
+            s = s.left_of(s.first_of(",}"));
+            if(s.ends_with(':'))
+                --s.len;
+        }
+    }
+    else if(has_all(RVAL))
+    {
+        _c4dbgp("RMAP|RVAL");
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(QMRK));
+        if( ! _is_scalar_next__rmap_val(s))
+            return false;
+        _RYML_WITH_TAB_TOKENS(else if(s.begins_with("-\t"))
+            return false;
+        )
+        _c4dbgp("RMAP|RVAL|FLOW");
+        if(has_none(RSEQIMAP))
+            s = s.left_of(s.first_of(",}"));
+        else
+            s = s.left_of(s.first_of(",]"));
+        s = s.left_of(s.find(" #")); // is there a comment?
+        s = s.left_of(s.find("\t#")); // is there a comment?
+        s = s.trim(_RYML_WITH_OR_WITHOUT_TAB_TOKENS(" \t", ' '));
+    }
+
+    if(s.empty())
+        return false;
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.str >= m_state->line_contents.rem.str);
+    _line_progressed(static_cast<size_t>(s.str - m_state->line_contents.rem.str) + s.len);
+
+    if(_at_line_end() && s != '~')
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    *scalar = s;
+    *quoted = false;
+    return true;
+}
+
+bool Parser::_scan_scalar_unk(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  has_any(RUNK));
+
+    csubstr s = m_state->line_contents.rem;
+    if(s.len == 0)
+        return false;
+    s = s.trim(" \t");
+    if(s.len == 0)
+        return false;
+
+    if(s.begins_with('\''))
+    {
+        _c4dbgp("got a ': scanning single-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_squot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('"'))
+    {
+        _c4dbgp("got a \": scanning double-quoted scalar");
+        m_state->scalar_col = m_state->line_contents.current_col(s);
+        *scalar = _scan_dquot_scalar();
+        *quoted = true;
+        return true;
+    }
+    else if(s.begins_with('|') || s.begins_with('>'))
+    {
+        *scalar = _scan_block();
+        *quoted = true;
+        return true;
+    }
+    else if(has_any(RTOP) && _is_doc_sep(s))
+    {
+        return false;
+    }
+
+    _c4dbgpf("RUNK '[{}]~~~{}~~~", s.len, s);
+    if( ! _is_scalar_next__runk(s))
+    {
+        _c4dbgp("RUNK: no scalar next");
+        return false;
+    }
+    size_t pos = s.find(" #");
+    if(pos != npos)
+        s = s.left_of(pos);
+    pos = s.find(": ");
+    if(pos != npos)
+        s = s.left_of(pos);
+    else if(s.ends_with(':'))
+        s = s.left_of(s.len-1);
+    _RYML_WITH_TAB_TOKENS(
+    else if((pos = s.find(":\t")) != npos) // TABS
+        s = s.left_of(pos);
+    )
+    else
+        s = s.left_of(s.first_of(','));
+    s = s.trim(" \t");
+    _c4dbgpf("RUNK: scalar='{}'", s);
+
+    if(s.empty())
+        return false;
+
+    m_state->scalar_col = m_state->line_contents.current_col(s);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.str >= m_state->line_contents.rem.str);
+    _line_progressed(static_cast<size_t>(s.str - m_state->line_contents.rem.str) + s.len);
+
+    if(_at_line_end() && s != '~')
+    {
+        _c4dbgpf("at line end. curr='{}'", s);
+        s = _extend_scanned_scalar(s);
+    }
+
+    _c4dbgpf("scalar was '{}'", s);
+
+    *scalar = s;
+    *quoted = false;
+    return true;
+}
+
+
+//-----------------------------------------------------------------------------
+
+csubstr Parser::_extend_scanned_scalar(csubstr s)
+{
+    if(has_all(RMAP|RKEY|QMRK))
+    {
+        size_t scalar_indentation = has_any(FLOW) ? 0 : m_state->scalar_col;
+        _c4dbgpf("extend_scalar: explicit key! indref={} scalar_indentation={} scalar_col={}", m_state->indref, scalar_indentation, m_state->scalar_col);
+        csubstr n = _scan_to_next_nonempty_line(scalar_indentation);
+        if(!n.empty())
+        {
+            substr full = _scan_complex_key(s, n).trimr(" \t\r\n");
+            if(full != s)
+                s = _filter_plain_scalar(full, scalar_indentation);
+        }
+    }
+    // deal with plain (unquoted) scalars that continue to the next line
+    else if(!s.begins_with_any("*")) // cannot be a plain scalar if it starts with * (that's an anchor reference)
+    {
+        _c4dbgpf("extend_scalar: line ended, scalar='{}'", s);
+        if(has_none(FLOW))
+        {
+            size_t scalar_indentation = m_state->indref + 1;
+            if(has_all(RUNK) && scalar_indentation == 1)
+                scalar_indentation = 0;
+            csubstr n = _scan_to_next_nonempty_line(scalar_indentation);
+            if(!n.empty())
+            {
+                _c4dbgpf("rscalar[IMPL]: state_indref={} state_indentation={} scalar_indentation={}", m_state->indref, m_state->line_contents.indentation, scalar_indentation);
+                _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.full.is_super(n));
+                substr full = _scan_plain_scalar_blck(s, n, scalar_indentation);
+                if(full.len >= s.len)
+                    s = _filter_plain_scalar(full, scalar_indentation);
+            }
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(FLOW));
+            csubstr n = _scan_to_next_nonempty_line(/*indentation*/0);
+            if(!n.empty())
+            {
+                _c4dbgp("rscalar[FLOW]");
+                substr full = _scan_plain_scalar_flow(s, n);
+                s = _filter_plain_scalar(full, /*indentation*/0);
+            }
+        }
+    }
+
+    return s;
+}
+
+
+//-----------------------------------------------------------------------------
+
+substr Parser::_scan_plain_scalar_flow(csubstr currscalar, csubstr peeked_line)
+{
+    static constexpr const csubstr chars = "[]{}?#,";
+    size_t pos = peeked_line.first_of(chars);
+    bool first = true;
+    while(pos != 0)
+    {
+        if(has_all(RMAP|RKEY) || has_any(RUNK))
+        {
+            csubstr tpkl = peeked_line.triml(' ').trimr("\r\n");
+            if(tpkl.begins_with(": ") || tpkl == ':')
+            {
+                _c4dbgpf("rscalar[FLOW]: map value starts on the peeked line: '{}'", peeked_line);
+                peeked_line = peeked_line.first(0);
+                break;
+            }
+            else
+            {
+                auto colon_pos = peeked_line.first_of_any(": ", ":");
+                if(colon_pos && colon_pos.pos < pos)
+                {
+                    peeked_line = peeked_line.first(colon_pos.pos);
+                    _c4dbgpf("rscalar[FLOW]: found colon at {}. peeked='{}'", colon_pos.pos, peeked_line);
+                    _RYML_CB_ASSERT(m_stack.m_callbacks, peeked_line.end() >= m_state->line_contents.rem.begin());
+                    _line_progressed(static_cast<size_t>(peeked_line.end() - m_state->line_contents.rem.begin()));
+                    break;
+                }
+            }
+        }
+        if(pos != npos)
+        {
+            _c4dbgpf("rscalar[FLOW]: found special character '{}' at {}, stopping: '{}'", peeked_line[pos], pos, peeked_line.left_of(pos).trimr("\r\n"));
+            peeked_line = peeked_line.left_of(pos);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, peeked_line.end() >= m_state->line_contents.rem.begin());
+            _line_progressed(static_cast<size_t>(peeked_line.end() - m_state->line_contents.rem.begin()));
+            break;
+        }
+        _c4dbgpf("rscalar[FLOW]: append another line, full: '{}'", peeked_line.trimr("\r\n"));
+        if(!first)
+        {
+            RYML_CHECK(_advance_to_peeked());
+        }
+        peeked_line = _scan_to_next_nonempty_line(/*indentation*/0);
+        if(peeked_line.empty())
+        {
+            _c4err("expected token or continuation");
+        }
+        pos = peeked_line.first_of(chars);
+        first = false;
+    }
+    substr full(m_buf.str + (currscalar.str - m_buf.str), m_buf.begin() + m_state->pos.offset);
+    full = full.trimr("\n\r ");
+    return full;
+}
+
+
+//-----------------------------------------------------------------------------
+
+substr Parser::_scan_plain_scalar_blck(csubstr currscalar, csubstr peeked_line, size_t indentation)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.is_super(currscalar));
+    // NOTE. there's a problem with _scan_to_next_nonempty_line(), as it counts newlines twice
+    // size_t offs = m_state->pos.offset;   // so we workaround by directly counting from the end of the given scalar
+    _RYML_CB_ASSERT(m_stack.m_callbacks, currscalar.end() >= m_buf.begin());
+    size_t offs = static_cast<size_t>(currscalar.end() - m_buf.begin());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, peeked_line.begins_with(' ', indentation));
+    while(true)
+    {
+        _c4dbgpf("rscalar[IMPL]: continuing... ref_indentation={}", indentation);
+        if(peeked_line.begins_with("...") || peeked_line.begins_with("---"))
+        {
+            _c4dbgpf("rscalar[IMPL]: document termination next -- bail now '{}'", peeked_line.trimr("\r\n"));
+            break;
+        }
+        else if(( ! peeked_line.begins_with(' ', indentation))) // is the line deindented?
+        {
+            if(!peeked_line.trim(" \r\n\t").empty()) // is the line not blank?
+            {
+                _c4dbgpf("rscalar[IMPL]: deindented line, not blank -- bail now '{}'", peeked_line.trimr("\r\n"));
+                break;
+            }
+            _c4dbgpf("rscalar[IMPL]: line is blank and has less indentation: ref={} line={}: '{}'", indentation, peeked_line.first_not_of(' ') == csubstr::npos ? 0 : peeked_line.first_not_of(' '), peeked_line.trimr("\r\n"));
+            _c4dbgpf("rscalar[IMPL]: ... searching for a line starting at indentation {}", indentation);
+            csubstr next_peeked = _scan_to_next_nonempty_line(indentation);
+            if(next_peeked.empty())
+            {
+                _c4dbgp("rscalar[IMPL]: ... finished.");
+                break;
+            }
+            _c4dbgp("rscalar[IMPL]: ... continuing.");
+            peeked_line = next_peeked;
+        }
+
+        _c4dbgpf("rscalar[IMPL]: line contents: '{}'", peeked_line.right_of(indentation, true).trimr("\r\n"));
+        size_t token_pos;
+        if(peeked_line.find(": ") != npos)
+        {
+            _line_progressed(peeked_line.find(": "));
+            _c4err("': ' is not a valid token in plain flow (unquoted) scalars");
+        }
+        else if(peeked_line.ends_with(':'))
+        {
+            _line_progressed(peeked_line.find(':'));
+            _c4err("lines cannot end with ':' in plain flow (unquoted) scalars");
+        }
+        else if((token_pos = peeked_line.find(" #")) != npos)
+        {
+            _line_progressed(token_pos);
+            break;
+            //_c4err("' #' is not a valid token in plain flow (unquoted) scalars");
+        }
+
+        _c4dbgpf("rscalar[IMPL]: append another line: (len={})'{}'", peeked_line.len, peeked_line.trimr("\r\n"));
+        if(!_advance_to_peeked())
+        {
+            _c4dbgp("rscalar[IMPL]: file finishes after the scalar");
+            break;
+        }
+        peeked_line = m_state->line_contents.rem;
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.offset >= offs);
+    substr full(m_buf.str + (currscalar.str - m_buf.str),
+                currscalar.len + (m_state->pos.offset - offs));
+    full = full.trimr("\r\n ");
+    return full;
+}
+
+substr Parser::_scan_complex_key(csubstr currscalar, csubstr peeked_line)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.is_super(currscalar));
+    // NOTE. there's a problem with _scan_to_next_nonempty_line(), as it counts newlines twice
+    // size_t offs = m_state->pos.offset;   // so we workaround by directly counting from the end of the given scalar
+    _RYML_CB_ASSERT(m_stack.m_callbacks, currscalar.end() >= m_buf.begin());
+    size_t offs = static_cast<size_t>(currscalar.end() - m_buf.begin());
+    while(true)
+    {
+        _c4dbgp("rcplxkey: continuing...");
+        if(peeked_line.begins_with("...") || peeked_line.begins_with("---"))
+        {
+            _c4dbgpf("rcplxkey: document termination next -- bail now '{}'", peeked_line.trimr("\r\n"));
+            break;
+        }
+        else
+        {
+            size_t pos = peeked_line.first_of("?:[]{}");
+            if(pos == csubstr::npos)
+            {
+                pos = peeked_line.find("- ");
+            }
+            if(pos != csubstr::npos)
+            {
+                _c4dbgpf("rcplxkey: found special characters at pos={}: '{}'", pos, peeked_line.trimr("\r\n"));
+                _line_progressed(pos);
+                break;
+            }
+        }
+
+        _c4dbgpf("rcplxkey: no special chars found '{}'", peeked_line.trimr("\r\n"));
+        csubstr next_peeked = _scan_to_next_nonempty_line(0);
+        if(next_peeked.empty())
+        {
+            _c4dbgp("rcplxkey: empty ... finished.");
+            break;
+        }
+        _c4dbgp("rcplxkey: ... continuing.");
+        peeked_line = next_peeked;
+
+        _c4dbgpf("rcplxkey: line contents: '{}'", peeked_line.trimr("\r\n"));
+        size_t colpos;
+        if((colpos = peeked_line.find(": ")) != npos)
+        {
+            _c4dbgp("rcplxkey: found ': ', stopping.");
+            _line_progressed(colpos);
+            break;
+        }
+        #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+        else if((colpos = peeked_line.ends_with(':')))
+        {
+            _c4dbgp("rcplxkey: ends with ':', stopping.");
+            _line_progressed(colpos);
+            break;
+        }
+        #endif
+        _c4dbgpf("rcplxkey: append another line: (len={})'{}'", peeked_line.len, peeked_line.trimr("\r\n"));
+        if(!_advance_to_peeked())
+        {
+            _c4dbgp("rcplxkey: file finishes after the scalar");
+            break;
+        }
+        peeked_line = m_state->line_contents.rem;
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.offset >= offs);
+    substr full(m_buf.str + (currscalar.str - m_buf.str),
+                currscalar.len + (m_state->pos.offset - offs));
+    return full;
+}
+
+//! scans to the next non-blank line starting with the given indentation
+csubstr Parser::_scan_to_next_nonempty_line(size_t indentation)
+{
+    csubstr next_peeked;
+    while(true)
+    {
+        _c4dbgpf("rscalar: ... curr offset: {} indentation={}", m_state->pos.offset, indentation);
+        next_peeked = _peek_next_line(m_state->pos.offset);
+        csubstr next_peeked_triml = next_peeked.triml(' ');
+        _c4dbgpf("rscalar: ... next peeked line='{}'", next_peeked.trimr("\r\n"));
+        if(next_peeked_triml.begins_with('#'))
+        {
+            _c4dbgp("rscalar: ... first non-space character is #");
+            return {};
+        }
+        else if(next_peeked.begins_with(' ', indentation))
+        {
+            _c4dbgpf("rscalar: ... begins at same indentation {}, assuming continuation", indentation);
+            _advance_to_peeked();
+            return next_peeked;
+        }
+        else   // check for de-indentation
+        {
+            csubstr trimmed = next_peeked_triml.trimr("\t\r\n");
+            _c4dbgpf("rscalar: ... deindented! trimmed='{}'", trimmed);
+            if(!trimmed.empty())
+            {
+                _c4dbgp("rscalar: ... and not empty. bailing out.");
+                return {};
+            }
+        }
+        if(!_advance_to_peeked())
+        {
+            _c4dbgp("rscalar: file finished");
+            return {};
+        }
+    }
+    return {};
+}
+
+// returns false when the file finished
+bool Parser::_advance_to_peeked()
+{
+    _line_progressed(m_state->line_contents.rem.len);
+    _line_ended(); // advances to the peeked-at line, consuming all remaining (probably newline) characters on the current line
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.rem.first_of("\r\n") == csubstr::npos);
+    _c4dbgpf("advance to peeked: scan more... pos={} len={}", m_state->pos.offset, m_buf.len);
+    _scan_line();  // puts the peeked-at line in the buffer
+    if(_finished_file())
+    {
+        _c4dbgp("rscalar: finished file!");
+        return false;
+    }
+    return true;
+}
+
+//-----------------------------------------------------------------------------
+
+C4_ALWAYS_INLINE size_t _extend_from_combined_newline(char nl, char following)
+{
+    return (nl == '\n' && following == '\r') || (nl == '\r' && following == '\n');
+}
+
+//! look for the next newline chars, and jump to the right of those
+csubstr from_next_line(csubstr rem)
+{
+    size_t nlpos = rem.first_of("\r\n");
+    if(nlpos == csubstr::npos)
+        return {};
+    const char nl = rem[nlpos];
+    rem = rem.right_of(nlpos);
+    if(rem.empty())
+        return {};
+    if(_extend_from_combined_newline(nl, rem.front()))
+        rem = rem.sub(1);
+    return rem;
+}
+
+csubstr Parser::_peek_next_line(size_t pos) const
+{
+    csubstr rem{}; // declare here because of the goto
+    size_t nlpos{}; // declare here because of the goto
+    pos = pos == npos ? m_state->pos.offset : pos;
+    if(pos >= m_buf.len)
+        goto next_is_empty;
+
+    // look for the next newline chars, and jump to the right of those
+    rem = from_next_line(m_buf.sub(pos));
+    if(rem.empty())
+        goto next_is_empty;
+
+    // now get everything up to and including the following newline chars
+    nlpos = rem.first_of("\r\n");
+    if((nlpos != csubstr::npos) && (nlpos + 1 < rem.len))
+        nlpos += _extend_from_combined_newline(rem[nlpos], rem[nlpos+1]);
+    rem = rem.left_of(nlpos, /*include_pos*/true);
+
+    _c4dbgpf("peek next line @ {}: (len={})'{}'", pos, rem.len, rem.trimr("\r\n"));
+    return rem;
+
+next_is_empty:
+    _c4dbgpf("peek next line @ {}: (len=0)''", pos);
+    return {};
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::LineContents::reset_with_next_line(csubstr buf, size_t offset)
+{
+    RYML_ASSERT(offset <= buf.len);
+    char const* C4_RESTRICT b = &buf[offset];
+    char const* C4_RESTRICT e = b;
+    // get the current line stripped of newline chars
+    while(e < buf.end() && (*e != '\n' && *e != '\r'))
+        ++e;
+    RYML_ASSERT(e >= b);
+    const csubstr stripped_ = buf.sub(offset, static_cast<size_t>(e - b));
+    // advance pos to include the first line ending
+    if(e != buf.end() && *e == '\r')
+        ++e;
+    if(e != buf.end() && *e == '\n')
+        ++e;
+    RYML_ASSERT(e >= b);
+    const csubstr full_ = buf.sub(offset, static_cast<size_t>(e - b));
+    reset(full_, stripped_);
+}
+
+void Parser::_scan_line()
+{
+    if(m_state->pos.offset >= m_buf.len)
+    {
+        m_state->line_contents.reset(m_buf.last(0), m_buf.last(0));
+        return;
+    }
+    m_state->line_contents.reset_with_next_line(m_buf, m_state->pos.offset);
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_line_progressed(size_t ahead)
+{
+    _c4dbgpf("line[{}] ({} cols) progressed by {}:  col {}-->{}   offset {}-->{}", m_state->pos.line, m_state->line_contents.full.len, ahead, m_state->pos.col, m_state->pos.col+ahead, m_state->pos.offset, m_state->pos.offset+ahead);
+    m_state->pos.offset += ahead;
+    m_state->pos.col += ahead;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.col <= m_state->line_contents.stripped.len+1);
+    m_state->line_contents.rem = m_state->line_contents.rem.sub(ahead);
+}
+
+void Parser::_line_ended()
+{
+    _c4dbgpf("line[{}] ({} cols) ended! offset {}-->{}", m_state->pos.line, m_state->line_contents.full.len, m_state->pos.offset, m_state->pos.offset+m_state->line_contents.full.len - m_state->line_contents.stripped.len);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.col == m_state->line_contents.stripped.len+1);
+    m_state->pos.offset += m_state->line_contents.full.len - m_state->line_contents.stripped.len;
+    ++m_state->pos.line;
+    m_state->pos.col = 1;
+}
+
+void Parser::_line_ended_undo()
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.col == 1u);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.line > 0u);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.offset >= m_state->line_contents.full.len - m_state->line_contents.stripped.len);
+    size_t delta = m_state->line_contents.full.len - m_state->line_contents.stripped.len;
+    _c4dbgpf("line[{}] undo ended! line {}-->{}, offset {}-->{}", m_state->pos.line, m_state->pos.line, m_state->pos.line - 1, m_state->pos.offset, m_state->pos.offset - delta);
+    m_state->pos.offset -= delta;
+    --m_state->pos.line;
+    m_state->pos.col = m_state->line_contents.stripped.len + 1u;
+    // don't forget to undo also the changes to the remainder of the line
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.offset >= m_buf.len || m_buf[m_state->pos.offset] == '\n' || m_buf[m_state->pos.offset] == '\r');
+    m_state->line_contents.rem = m_buf.sub(m_state->pos.offset, 0);
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_set_indentation(size_t indentation)
+{
+    m_state->indref = indentation;
+    _c4dbgpf("state[{}]: saving indentation: {}", m_state-m_stack.begin(), m_state->indref);
+}
+
+void Parser::_save_indentation(size_t behind)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->line_contents.rem.begin() >= m_state->line_contents.full.begin());
+    m_state->indref = static_cast<size_t>(m_state->line_contents.rem.begin() - m_state->line_contents.full.begin());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, behind <= m_state->indref);
+    m_state->indref -= behind;
+    _c4dbgpf("state[{}]: saving indentation: {}", m_state-m_stack.begin(), m_state->indref);
+}
+
+bool Parser::_maybe_set_indentation_from_anchor_or_tag()
+{
+    if(m_key_anchor.not_empty())
+    {
+        _c4dbgpf("set indentation from key anchor: {}", m_key_anchor_indentation);
+        _set_indentation(m_key_anchor_indentation); // this is the column where the anchor starts
+        return true;
+    }
+    else if(m_key_tag.not_empty())
+    {
+        _c4dbgpf("set indentation from key tag: {}", m_key_tag_indentation);
+        _set_indentation(m_key_tag_indentation); // this is the column where the tag starts
+        return true;
+    }
+    return false;
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_write_key_anchor(size_t node_id)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->has_key(node_id));
+    if( ! m_key_anchor.empty())
+    {
+        _c4dbgpf("node={}: set key anchor to '{}'", node_id, m_key_anchor);
+        m_tree->set_key_anchor(node_id, m_key_anchor);
+        m_key_anchor.clear();
+        m_key_anchor_was_before = false;
+        m_key_anchor_indentation = 0;
+    }
+    else if( ! m_tree->is_key_quoted(node_id))
+    {
+        csubstr r = m_tree->key(node_id);
+        if(r.begins_with('*'))
+        {
+            _c4dbgpf("node={}: set key reference: '{}'", node_id, r);
+            m_tree->set_key_ref(node_id, r.sub(1));
+        }
+        else if(r == "<<")
+        {
+            m_tree->set_key_ref(node_id, r);
+            _c4dbgpf("node={}: it's an inheriting reference", node_id);
+            if(m_tree->is_seq(node_id))
+            {
+                _c4dbgpf("node={}: inheriting from seq of {}", node_id, m_tree->num_children(node_id));
+                for(size_t i = m_tree->first_child(node_id); i != NONE; i = m_tree->next_sibling(i))
+                {
+                    if( ! (m_tree->val(i).begins_with('*')))
+                        _c4err("malformed reference: '{}'", m_tree->val(i));
+                }
+            }
+            else if( ! m_tree->val(node_id).begins_with('*'))
+            {
+                 _c4err("malformed reference: '{}'", m_tree->val(node_id));
+            }
+            //m_tree->set_key_ref(node_id, r);
+        }
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_write_val_anchor(size_t node_id)
+{
+    if( ! m_val_anchor.empty())
+    {
+        _c4dbgpf("node={}: set val anchor to '{}'", node_id, m_val_anchor);
+        m_tree->set_val_anchor(node_id, m_val_anchor);
+        m_val_anchor.clear();
+    }
+    csubstr r = m_tree->has_val(node_id) ? m_tree->val(node_id) : "";
+    if(!m_tree->is_val_quoted(node_id) && r.begins_with('*'))
+    {
+        _c4dbgpf("node={}: set val reference: '{}'", node_id, r);
+        RYML_CHECK(!m_tree->has_val_anchor(node_id));
+        m_tree->set_val_ref(node_id, r.sub(1));
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_push_level(bool explicit_flow_chars)
+{
+    _c4dbgpf("pushing level! currnode={}  currlevel={} stacksize={} stackcap={}", m_state->node_id, m_state->level, m_stack.size(), m_stack.capacity());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state == &m_stack.top());
+    if(node(m_state) == nullptr)
+    {
+        _c4dbgp("pushing level! actually no, current node is null");
+        //_RYML_CB_ASSERT(m_stack.m_callbacks,  ! explicit_flow_chars);
+        return;
+    }
+    flag_t st = RUNK;
+    if(explicit_flow_chars || has_all(FLOW))
+    {
+        st |= FLOW;
+    }
+    m_stack.push_top();
+    m_state = &m_stack.top();
+    set_flags(st);
+    m_state->node_id = (size_t)NONE;
+    m_state->indref = (size_t)NONE;
+    ++m_state->level;
+    _c4dbgpf("pushing level: now, currlevel={}", m_state->level);
+}
+
+void Parser::_pop_level()
+{
+    _c4dbgpf("popping level! currnode={} currlevel={}", m_state->node_id, m_state->level);
+    if(has_any(RMAP) || m_tree->is_map(m_state->node_id))
+    {
+        _stop_map();
+    }
+    if(has_any(RSEQ) || m_tree->is_seq(m_state->node_id))
+    {
+        _stop_seq();
+    }
+    if(m_tree->is_doc(m_state->node_id))
+    {
+        _stop_doc();
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_stack.size() > 1);
+    _prepare_pop();
+    m_stack.pop();
+    m_state = &m_stack.top();
+    /*if(has_any(RMAP))
+    {
+        _toggle_key_val();
+    }*/
+    if(m_state->line_contents.indentation == 0)
+    {
+        //_RYML_CB_ASSERT(m_stack.m_callbacks, has_none(RTOP));
+        add_flags(RTOP);
+    }
+    _c4dbgpf("popping level: now, currnode={} currlevel={}", m_state->node_id, m_state->level);
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_start_unk(bool /*as_child*/)
+{
+    _c4dbgp("start_unk");
+    _push_level();
+    _move_scalar_from_top();
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_start_doc(bool as_child)
+{
+    _c4dbgpf("start_doc (as child={})", as_child);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_stack.bottom()) == node(m_root_id));
+    size_t parent_id = m_stack.size() < 2 ? m_root_id : m_stack.top(1).node_id;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, parent_id != NONE);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_root(parent_id));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_state) == nullptr || node(m_state) == node(m_root_id));
+    if(as_child)
+    {
+        _c4dbgpf("start_doc: parent={}", parent_id);
+        if( ! m_tree->is_stream(parent_id))
+        {
+            _c4dbgp("start_doc: rearranging with root as STREAM");
+            m_tree->set_root_as_stream();
+        }
+        m_state->node_id = m_tree->append_child(parent_id);
+        m_tree->to_doc(m_state->node_id);
+    }
+    #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+    else
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_seq(parent_id) || m_tree->empty(parent_id));
+        m_state->node_id = parent_id;
+        if( ! m_tree->is_doc(parent_id))
+        {
+            m_tree->to_doc(parent_id, DOC);
+        }
+    }
+    #endif
+    _c4dbgpf("start_doc: id={}", m_state->node_id);
+    add_flags(RUNK|RTOP|NDOC);
+    _handle_types();
+    rem_flags(NDOC);
+}
+
+void Parser::_stop_doc()
+{
+    size_t doc_node = m_state->node_id;
+    _c4dbgpf("stop_doc[{}]", doc_node);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_doc(doc_node));
+    if(!m_tree->is_seq(doc_node) && !m_tree->is_map(doc_node) && !m_tree->is_val(doc_node))
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(SSCL));
+        _c4dbgpf("stop_doc[{}]: there was nothing; adding null val", doc_node);
+        m_tree->to_val(doc_node, {}, DOC);
+    }
+}
+
+void Parser::_end_stream()
+{
+    _c4dbgpf("end_stream, level={} node_id={}", m_state->level, m_state->node_id);
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! m_stack.empty());
+    NodeData *added = nullptr;
+    if(has_any(SSCL))
+    {
+        if(m_tree->is_seq(m_state->node_id))
+        {
+            _c4dbgp("append val...");
+            added = _append_val(_consume_scalar());
+        }
+        else if(m_tree->is_map(m_state->node_id))
+        {
+            _c4dbgp("append null key val...");
+            added = _append_key_val_null(m_state->line_contents.rem.str);
+            #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+            if(has_any(RSEQIMAP))
+            {
+                _stop_seqimap();
+                _pop_level();
+            }
+            #endif
+        }
+        else if(m_tree->is_doc(m_state->node_id) || m_tree->type(m_state->node_id) == NOTYPE)
+        {
+            NodeType_e quoted = has_any(QSCL) ? VALQUO : NOTYPE; // do this before consuming the scalar
+            csubstr scalar = _consume_scalar();
+            _c4dbgpf("node[{}]: to docval '{}'{}", m_state->node_id, scalar, quoted == VALQUO ? ", quoted" : "");
+            m_tree->to_val(m_state->node_id, scalar, DOC|quoted);
+            added = m_tree->get(m_state->node_id);
+        }
+        else
+        {
+            _c4err("internal error");
+        }
+    }
+    else if(has_all(RSEQ|RVAL) && has_none(FLOW))
+    {
+        _c4dbgp("add last...");
+        added = _append_val_null(m_state->line_contents.rem.str);
+    }
+    else if(!m_val_tag.empty() && (m_tree->is_doc(m_state->node_id) || m_tree->type(m_state->node_id) == NOTYPE))
+    {
+        csubstr scalar = m_state->line_contents.rem.first(0);
+        _c4dbgpf("node[{}]: add null scalar as docval", m_state->node_id);
+        m_tree->to_val(m_state->node_id, scalar, DOC);
+        added = m_tree->get(m_state->node_id);
+    }
+
+    if(added)
+    {
+        size_t added_id = m_tree->id(added);
+        if(m_tree->is_seq(m_state->node_id) || m_tree->is_doc(m_state->node_id))
+        {
+            if(!m_key_anchor.empty())
+            {
+                _c4dbgpf("node[{}]: move key to val anchor: '{}'", added_id, m_key_anchor);
+                m_val_anchor = m_key_anchor;
+                m_key_anchor = {};
+            }
+            if(!m_key_tag.empty())
+            {
+                _c4dbgpf("node[{}]: move key to val tag: '{}'", added_id, m_key_tag);
+                m_val_tag = m_key_tag;
+                m_key_tag = {};
+            }
+        }
+        #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+        if(!m_key_anchor.empty())
+        {
+            _c4dbgpf("node[{}]: set key anchor='{}'", added_id, m_key_anchor);
+            m_tree->set_key_anchor(added_id, m_key_anchor);
+            m_key_anchor = {};
+        }
+        #endif
+        if(!m_val_anchor.empty())
+        {
+            _c4dbgpf("node[{}]: set val anchor='{}'", added_id, m_val_anchor);
+            m_tree->set_val_anchor(added_id, m_val_anchor);
+            m_val_anchor = {};
+        }
+        #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+        if(!m_key_tag.empty())
+        {
+            _c4dbgpf("node[{}]: set key tag='{}' -> '{}'", added_id, m_key_tag, normalize_tag(m_key_tag));
+            m_tree->set_key_tag(added_id, normalize_tag(m_key_tag));
+            m_key_tag = {};
+        }
+        #endif
+        if(!m_val_tag.empty())
+        {
+            _c4dbgpf("node[{}]: set val tag='{}' -> '{}'", added_id, m_val_tag, normalize_tag(m_val_tag));
+            m_tree->set_val_tag(added_id, normalize_tag(m_val_tag));
+            m_val_tag = {};
+        }
+    }
+
+    while(m_stack.size() > 1)
+    {
+        _c4dbgpf("popping level: {} (stack sz={})", m_state->level, m_stack.size());
+        _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_any(SSCL, &m_stack.top()));
+        if(has_all(RSEQ|FLOW))
+            _err("closing ] not found");
+        _pop_level();
+    }
+    add_flags(NDOC);
+}
+
+void Parser::_start_new_doc(csubstr rem)
+{
+    _c4dbgp("_start_new_doc");
+    _RYML_CB_ASSERT(m_stack.m_callbacks, rem.begins_with("---"));
+    C4_UNUSED(rem);
+
+    _end_stream();
+
+    size_t indref = m_state->indref;
+    _c4dbgpf("start a document, indentation={}", indref);
+    _line_progressed(3);
+    _push_level();
+    _start_doc();
+    _set_indentation(indref);
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_start_map(bool as_child)
+{
+    _c4dbgpf("start_map (as child={})", as_child);
+    addrem_flags(RMAP|RVAL, RKEY|RUNK);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_stack.bottom()) == node(m_root_id));
+    size_t parent_id = m_stack.size() < 2 ? m_root_id : m_stack.top(1).node_id;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, parent_id != NONE);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_state) == nullptr || node(m_state) == node(m_root_id));
+    if(as_child)
+    {
+        m_state->node_id = m_tree->append_child(parent_id);
+        if(has_all(SSCL))
+        {
+            type_bits key_quoted = NOTYPE;
+            if(m_state->flags & QSCL) // before consuming the scalar
+                key_quoted |= KEYQUO;
+            csubstr key = _consume_scalar();
+            m_tree->to_map(m_state->node_id, key, key_quoted);
+            _c4dbgpf("start_map: id={} key='{}'", m_state->node_id, m_tree->key(m_state->node_id));
+            _write_key_anchor(m_state->node_id);
+            if( ! m_key_tag.empty())
+            {
+                _c4dbgpf("node[{}]: set key tag='{}' -> '{}'", m_state->node_id, m_key_tag, normalize_tag(m_key_tag));
+                m_tree->set_key_tag(m_state->node_id, normalize_tag(m_key_tag));
+                m_key_tag.clear();
+            }
+        }
+        else
+        {
+            m_tree->to_map(m_state->node_id);
+            _c4dbgpf("start_map: id={}", m_state->node_id);
+        }
+        m_tree->_p(m_state->node_id)->m_val.scalar.str = m_state->line_contents.rem.str;
+        _write_val_anchor(m_state->node_id);
+    }
+    else
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, parent_id != NONE);
+        m_state->node_id = parent_id;
+        _c4dbgpf("start_map: id={}", m_state->node_id);
+        type_bits as_doc = 0;
+        if(m_tree->is_doc(m_state->node_id))
+            as_doc |= DOC;
+        if(!m_tree->is_map(parent_id))
+        {
+            RYML_CHECK(!m_tree->has_children(parent_id));
+            m_tree->to_map(parent_id, as_doc);
+        }
+        else
+        {
+            m_tree->_add_flags(parent_id, as_doc);
+        }
+        _move_scalar_from_top();
+        if(m_key_anchor.not_empty())
+            m_key_anchor_was_before = true;
+        _write_val_anchor(parent_id);
+        if(m_stack.size() >= 2)
+        {
+            State const& parent_state = m_stack.top(1);
+            if(parent_state.flags & RSET)
+                add_flags(RSET);
+        }
+        m_tree->_p(parent_id)->m_val.scalar.str = m_state->line_contents.rem.str;
+    }
+    if( ! m_val_tag.empty())
+    {
+        _c4dbgpf("node[{}]: set val tag='{}' -> '{}'", m_state->node_id, m_val_tag, normalize_tag(m_val_tag));
+        m_tree->set_val_tag(m_state->node_id, normalize_tag(m_val_tag));
+        m_val_tag.clear();
+    }
+}
+
+void Parser::_start_map_unk(bool as_child)
+{
+    if(!m_key_anchor_was_before)
+    {
+        _c4dbgpf("stash key anchor before starting map... '{}'", m_key_anchor);
+        csubstr ka = m_key_anchor;
+        m_key_anchor = {};
+        _start_map(as_child);
+        m_key_anchor = ka;
+    }
+    else
+    {
+        _start_map(as_child);
+        m_key_anchor_was_before = false;
+    }
+    if(m_key_tag2.not_empty())
+    {
+        m_key_tag = m_key_tag2;
+        m_key_tag_indentation = m_key_tag2_indentation;
+        m_key_tag2.clear();
+        m_key_tag2_indentation = 0;
+    }
+}
+
+void Parser::_stop_map()
+{
+    _c4dbgpf("stop_map[{}]", m_state->node_id);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_map(m_state->node_id));
+    if(has_all(QMRK|RKEY) && !has_all(SSCL))
+    {
+        _c4dbgpf("stop_map[{}]: RKEY", m_state->node_id);
+        _store_scalar_null(m_state->line_contents.rem.str);
+        _append_key_val_null(m_state->line_contents.rem.str);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_start_seq(bool as_child)
+{
+    _c4dbgpf("start_seq (as child={})", as_child);
+    if(has_all(RTOP|RUNK))
+    {
+        _c4dbgpf("start_seq: moving key tag to val tag: '{}'", m_key_tag);
+        m_val_tag = m_key_tag;
+        m_key_tag.clear();
+    }
+    addrem_flags(RSEQ|RVAL, RUNK);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_stack.bottom()) == node(m_root_id));
+    size_t parent_id = m_stack.size() < 2 ? m_root_id : m_stack.top(1).node_id;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, parent_id != NONE);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_state) == nullptr || node(m_state) == node(m_root_id));
+    if(as_child)
+    {
+        m_state->node_id = m_tree->append_child(parent_id);
+        if(has_all(SSCL))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_map(parent_id));
+            type_bits key_quoted = 0;
+            if(m_state->flags & QSCL) // before consuming the scalar
+                key_quoted |= KEYQUO;
+            csubstr key = _consume_scalar();
+            m_tree->to_seq(m_state->node_id, key, key_quoted);
+            _c4dbgpf("start_seq: id={} name='{}'", m_state->node_id, m_tree->key(m_state->node_id));
+            _write_key_anchor(m_state->node_id);
+            if( ! m_key_tag.empty())
+            {
+                _c4dbgpf("start_seq[{}]: set key tag='{}' -> '{}'", m_state->node_id, m_key_tag, normalize_tag(m_key_tag));
+                m_tree->set_key_tag(m_state->node_id, normalize_tag(m_key_tag));
+                m_key_tag.clear();
+            }
+        }
+        else
+        {
+            type_bits as_doc = 0;
+            _RYML_CB_ASSERT(m_stack.m_callbacks, !m_tree->is_doc(m_state->node_id));
+            m_tree->to_seq(m_state->node_id, as_doc);
+            _c4dbgpf("start_seq: id={}{}", m_state->node_id, as_doc ? " as doc" : "");
+        }
+        _write_val_anchor(m_state->node_id);
+        m_tree->_p(m_state->node_id)->m_val.scalar.str = m_state->line_contents.rem.str;
+    }
+    else
+    {
+        m_state->node_id = parent_id;
+        type_bits as_doc = 0;
+        if(m_tree->is_doc(m_state->node_id))
+            as_doc |= DOC;
+        if(!m_tree->is_seq(parent_id))
+        {
+            RYML_CHECK(!m_tree->has_children(parent_id));
+            m_tree->to_seq(parent_id, as_doc);
+        }
+        else
+        {
+            m_tree->_add_flags(parent_id, as_doc);
+        }
+        _move_scalar_from_top();
+        _c4dbgpf("start_seq: id={}{}", m_state->node_id, as_doc ? " as_doc" : "");
+        _write_val_anchor(parent_id);
+        m_tree->_p(parent_id)->m_val.scalar.str = m_state->line_contents.rem.str;
+    }
+    if( ! m_val_tag.empty())
+    {
+        _c4dbgpf("start_seq[{}]: set val tag='{}' -> '{}'", m_state->node_id, m_val_tag, normalize_tag(m_val_tag));
+        m_tree->set_val_tag(m_state->node_id, normalize_tag(m_val_tag));
+        m_val_tag.clear();
+    }
+}
+
+void Parser::_stop_seq()
+{
+    _c4dbgp("stop_seq");
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_seq(m_state->node_id));
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_start_seqimap()
+{
+    _c4dbgpf("start_seqimap at node={}. has_children={}", m_state->node_id, m_tree->has_children(m_state->node_id));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RSEQ|FLOW));
+    // create a map, and turn the last scalar of this sequence
+    // into the key of the map's first child. This scalar was
+    // understood to be a value in the sequence, but it is
+    // actually a key of a map, implicitly opened here.
+    // Eg [val, key: val]
+    //
+    // Yep, YAML is crazy.
+    if(m_tree->has_children(m_state->node_id) && m_tree->has_val(m_tree->last_child(m_state->node_id)))
+    {
+        size_t prev = m_tree->last_child(m_state->node_id);
+        NodeType ty = m_tree->_p(prev)->m_type; // don't use type() because it masks out the quotes
+        NodeScalar tmp = m_tree->valsc(prev);
+        _c4dbgpf("has children and last child={} has val. saving the scalars, val='{}' quoted={}", prev, tmp.scalar, ty.is_val_quoted());
+        m_tree->remove(prev);
+        _push_level();
+        _start_map();
+        _store_scalar(tmp.scalar, ty.is_val_quoted());
+        m_key_anchor = tmp.anchor;
+        m_key_tag = tmp.tag;
+    }
+    else
+    {
+        _c4dbgpf("node {} has no children yet, using empty key", m_state->node_id);
+        _push_level();
+        _start_map();
+        _store_scalar_null(m_state->line_contents.rem.str);
+    }
+    add_flags(RSEQIMAP|FLOW);
+}
+
+void Parser::_stop_seqimap()
+{
+    _c4dbgp("stop_seqimap");
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(RSEQIMAP));
+}
+
+
+//-----------------------------------------------------------------------------
+NodeData* Parser::_append_val(csubstr val, flag_t quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks,  ! has_all(SSCL));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node(m_state) != nullptr);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_seq(m_state->node_id));
+    type_bits additional_flags = quoted ? VALQUO : NOTYPE;
+    _c4dbgpf("append val: '{}' to parent id={} (level={}){}", val, m_state->node_id, m_state->level, quoted ? " VALQUO!" : "");
+    size_t nid = m_tree->append_child(m_state->node_id);
+    m_tree->to_val(nid, val, additional_flags);
+
+    _c4dbgpf("append val: id={} val='{}'", nid, m_tree->get(nid)->m_val.scalar);
+    if( ! m_val_tag.empty())
+    {
+        _c4dbgpf("append val[{}]: set val tag='{}' -> '{}'", nid, m_val_tag, normalize_tag(m_val_tag));
+        m_tree->set_val_tag(nid, normalize_tag(m_val_tag));
+        m_val_tag.clear();
+    }
+    _write_val_anchor(nid);
+    return m_tree->get(nid);
+}
+
+NodeData* Parser::_append_key_val(csubstr val, flag_t val_quoted)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_tree->is_map(m_state->node_id));
+    type_bits additional_flags = 0;
+    if(m_state->flags & QSCL)
+        additional_flags |= KEYQUO;
+    if(val_quoted)
+        additional_flags |= VALQUO;
+
+    csubstr key = _consume_scalar();
+    _c4dbgpf("append keyval: '{}' '{}' to parent id={} (level={}){}{}", key, val, m_state->node_id, m_state->level, (additional_flags & KEYQUO) ? " KEYQUO!" : "", (additional_flags & VALQUO) ? " VALQUO!" : "");
+    size_t nid = m_tree->append_child(m_state->node_id);
+    m_tree->to_keyval(nid, key, val, additional_flags);
+    _c4dbgpf("append keyval: id={} key='{}' val='{}'", nid, m_tree->key(nid), m_tree->val(nid));
+    if( ! m_key_tag.empty())
+    {
+        _c4dbgpf("append keyval[{}]: set key tag='{}' -> '{}'", nid, m_key_tag, normalize_tag(m_key_tag));
+        m_tree->set_key_tag(nid, normalize_tag(m_key_tag));
+        m_key_tag.clear();
+    }
+    if( ! m_val_tag.empty())
+    {
+        _c4dbgpf("append keyval[{}]: set val tag='{}' -> '{}'", nid, m_val_tag, normalize_tag(m_val_tag));
+        m_tree->set_val_tag(nid, normalize_tag(m_val_tag));
+        m_val_tag.clear();
+    }
+    _write_key_anchor(nid);
+    _write_val_anchor(nid);
+    rem_flags(QMRK);
+    return m_tree->get(nid);
+}
+
+
+//-----------------------------------------------------------------------------
+void Parser::_store_scalar(csubstr s, flag_t is_quoted)
+{
+    _c4dbgpf("state[{}]: storing scalar '{}' (flag: {}) (old scalar='{}')",
+             m_state-m_stack.begin(), s, m_state->flags & SSCL, m_state->scalar);
+    RYML_CHECK(has_none(SSCL));
+    add_flags(SSCL | (is_quoted * QSCL));
+    m_state->scalar = s;
+}
+
+csubstr Parser::_consume_scalar()
+{
+    _c4dbgpf("state[{}]: consuming scalar '{}' (flag: {}))", m_state-m_stack.begin(), m_state->scalar, m_state->flags & SSCL);
+    RYML_CHECK(m_state->flags & SSCL);
+    csubstr s = m_state->scalar;
+    rem_flags(SSCL | QSCL);
+    m_state->scalar.clear();
+    return s;
+}
+
+void Parser::_move_scalar_from_top()
+{
+    if(m_stack.size() < 2) return;
+    State &prev = m_stack.top(1);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state == &m_stack.top());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state != &prev);
+    if(prev.flags & SSCL)
+    {
+        _c4dbgpf("moving scalar '{}' from state[{}] to state[{}] (overwriting '{}')", prev.scalar, &prev-m_stack.begin(), m_state-m_stack.begin(), m_state->scalar);
+        add_flags(prev.flags & (SSCL | QSCL));
+        m_state->scalar = prev.scalar;
+        rem_flags(SSCL | QSCL, &prev);
+        prev.scalar.clear();
+    }
+}
+
+//-----------------------------------------------------------------------------
+/** @todo this function is a monster and needs love. Likely, it needs
+ * to be split like _scan_scalar_*() */
+bool Parser::_handle_indentation()
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(FLOW));
+    if( ! _at_line_begin())
+        return false;
+
+    size_t ind = m_state->line_contents.indentation;
+    csubstr rem = m_state->line_contents.rem;
+    /** @todo instead of trimming, we should use the indentation index from above */
+    csubstr remt = rem.triml(' ');
+
+    if(remt.empty() || remt.begins_with('#')) // this is a blank or comment line
+    {
+        _line_progressed(rem.size());
+        return true;
+    }
+
+    _c4dbgpf("indentation? ind={} indref={}", ind, m_state->indref);
+    if(ind == m_state->indref)
+    {
+        _c4dbgpf("same indentation: {}", ind);
+        if(!rem.sub(ind).begins_with('-'))
+        {
+            _c4dbgp("does not begin with -");
+            if(has_any(RMAP))
+            {
+                if(has_all(SSCL|RVAL))
+                {
+                    _c4dbgp("add with null val");
+                    _append_key_val_null(rem.str + ind - 1);
+                    addrem_flags(RKEY, RVAL);
+                }
+            }
+            else if(has_any(RSEQ))
+            {
+                if(m_stack.size() > 2) // do not pop to root level
+                {
+                    if(has_any(RNXT))
+                    {
+                        _c4dbgp("end the indentless seq");
+                        _pop_level();
+                        return true;
+                    }
+                    else if(has_any(RVAL))
+                    {
+                        _c4dbgp("add with null val");
+                        _append_val_null(rem.str);
+                        _c4dbgp("end the indentless seq");
+                        _pop_level();
+                        return true;
+                    }
+                }
+            }
+        }
+        _line_progressed(ind);
+        return ind > 0;
+    }
+    else if(ind < m_state->indref)
+    {
+        _c4dbgpf("smaller indentation ({} < {})!!!", ind, m_state->indref);
+        if(has_all(RVAL))
+        {
+            _c4dbgp("there was an empty val -- appending");
+            if(has_all(RMAP))
+            {
+                _RYML_CB_ASSERT(m_stack.m_callbacks, has_all(SSCL));
+                _append_key_val_null(rem.sub(ind).str - 1);
+            }
+            else if(has_all(RSEQ))
+            {
+                _RYML_CB_ASSERT(m_stack.m_callbacks, has_none(SSCL));
+                _append_val_null(rem.sub(ind).str - 1);
+            }
+        }
+        // search the stack frame to jump to based on its indentation
+        State const* popto = nullptr;
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_stack.is_contiguous()); // this search relies on the stack being contiguous
+        for(State const* s = m_state-1; s >= m_stack.begin(); --s)
+        {
+            _c4dbgpf("searching for state with indentation {}. curr={} (level={},node={})", ind, s->indref, s->level, s->node_id);
+            if(s->indref == ind)
+            {
+                _c4dbgpf("gotit!!! level={} node={}", s->level, s->node_id);
+                popto = s;
+                // while it may be tempting to think we're done at this
+                // point, we must still determine whether we're jumping to a
+                // parent with the same indentation. Consider this case with
+                // an indentless sequence:
+                //
+                // product:
+                // - sku: BL394D
+                //   quantity: 4
+                //   description: Basketball
+                //   price: 450.00
+                // - sku: BL4438H
+                //   quantity: 1
+                //   description: Super Hoop
+                //   price: 2392.00  # jumping one level here would be wrong.
+                // tax: 1234.5       # we must jump two levels
+                if(popto > m_stack.begin())
+                {
+                    auto parent = popto - 1;
+                    if(parent->indref == popto->indref)
+                    {
+                        _c4dbgpf("the parent (level={},node={}) has the same indentation ({}). is this in an indentless sequence?", parent->level, parent->node_id, popto->indref);
+                        _c4dbgpf("isseq(popto)={} ismap(parent)={}", m_tree->is_seq(popto->node_id), m_tree->is_map(parent->node_id));
+                        if(m_tree->is_seq(popto->node_id) && m_tree->is_map(parent->node_id))
+                        {
+                            if( ! remt.begins_with('-'))
+                            {
+                                _c4dbgp("this is an indentless sequence");
+                                popto = parent;
+                            }
+                            else
+                            {
+                                _c4dbgp("not an indentless sequence");
+                            }
+                        }
+                    }
+                }
+                break;
+            }
+        }
+        if(!popto || popto >= m_state || popto->level >= m_state->level)
+        {
+            _c4err("parse error: incorrect indentation?");
+        }
+        _c4dbgpf("popping {} levels: from level {} to level {}", m_state->level-popto->level, m_state->level, popto->level);
+        while(m_state != popto)
+        {
+            _c4dbgpf("popping level {} (indentation={})", m_state->level, m_state->indref);
+            _pop_level();
+        }
+        _RYML_CB_ASSERT(m_stack.m_callbacks, ind == m_state->indref);
+        _line_progressed(ind);
+        return true;
+    }
+    else
+    {
+        _c4dbgpf("larger indentation ({} > {})!!!", ind, m_state->indref);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, ind > m_state->indref);
+        if(has_all(RMAP|RVAL))
+        {
+            if(_is_scalar_next__rmap_val(remt) && remt.first_of(":?") == npos)
+            {
+                _c4dbgpf("actually it seems a value: '{}'", remt);
+            }
+            else
+            {
+                addrem_flags(RKEY, RVAL);
+                _start_unk();
+                //_move_scalar_from_top();
+                _line_progressed(ind);
+                _save_indentation();
+                return true;
+            }
+        }
+        else if(has_all(RSEQ|RVAL))
+        {
+            // nothing to do here
+        }
+        else
+        {
+            _c4err("parse error - indentation should not increase at this point");
+        }
+    }
+
+    return false;
+}
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_scan_comment()
+{
+    csubstr s = m_state->line_contents.rem;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.begins_with('#'));
+    _line_progressed(s.len);
+    // skip the # character
+    s = s.sub(1);
+    // skip leading whitespace
+    s = s.right_of(s.first_not_of(' '), /*include_pos*/true);
+    _c4dbgpf("comment was '{}'", s);
+    return s;
+}
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_scan_squot_scalar()
+{
+    // quoted scalars can spread over multiple lines!
+    // nice explanation here: http://yaml-multiline.info/
+
+    // a span to the end of the file
+    size_t b = m_state->pos.offset;
+    substr s = m_buf.sub(b);
+    if(s.begins_with(' '))
+    {
+        s = s.triml(' ');
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.sub(b).is_super(s));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.begin() >= m_buf.sub(b).begin());
+        _line_progressed((size_t)(s.begin() - m_buf.sub(b).begin()));
+    }
+    b = m_state->pos.offset; // take this into account
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.begins_with('\''));
+
+    // skip the opening quote
+    _line_progressed(1);
+    s = s.sub(1);
+
+    bool needs_filter = false;
+
+    size_t numlines = 1; // we already have one line
+    size_t pos = npos; // find the pos of the matching quote
+    while( ! _finished_file())
+    {
+        const csubstr line = m_state->line_contents.rem;
+        bool line_is_blank = true;
+        _c4dbgpf("scanning single quoted scalar @ line[{}]: ~~~{}~~~", m_state->pos.line, line);
+        for(size_t i = 0; i < line.len; ++i)
+        {
+            const char curr = line.str[i];
+            if(curr == '\'') // single quotes are escaped with two single quotes
+            {
+                const char next = i+1 < line.len ? line.str[i+1] : '~';
+                if(next != '\'') // so just look for the first quote
+                {                // without another after it
+                    pos = i;
+                    break;
+                }
+                else
+                {
+                    needs_filter = true; // needs filter to remove escaped quotes
+                    ++i; // skip the escaped quote
+                }
+            }
+            else if(curr != ' ')
+            {
+                line_is_blank = false;
+            }
+        }
+
+        // leading whitespace also needs filtering
+        needs_filter = needs_filter
+            || (numlines > 1)
+            || line_is_blank
+            || (_at_line_begin() && line.begins_with(' '));
+
+        if(pos == npos)
+        {
+            _line_progressed(line.len);
+            ++numlines;
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, pos >= 0 && pos < m_buf.len);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf[m_state->pos.offset + pos] == '\'');
+            _line_progressed(pos + 1); // progress beyond the quote
+            pos = m_state->pos.offset - b - 1; // but we stop before it
+            break;
+        }
+
+        _line_ended();
+        _scan_line();
+    }
+
+    if(pos == npos)
+    {
+        _c4err("reached end of file while looking for closing quote");
+    }
+    else
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, pos > 0);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.end() >= m_buf.begin() && s.end() <= m_buf.end());
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.end() == m_buf.end() || *s.end() == '\'');
+        s = s.sub(0, pos-1);
+    }
+
+    if(needs_filter)
+    {
+        csubstr ret = _filter_squot_scalar(s);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, ret.len <= s.len || s.empty() || s.trim(' ').empty());
+        _c4dbgpf("final scalar: \"{}\"", ret);
+        return ret;
+    }
+
+    _c4dbgpf("final scalar: \"{}\"", s);
+
+    return s;
+}
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_scan_dquot_scalar()
+{
+    // quoted scalars can spread over multiple lines!
+    // nice explanation here: http://yaml-multiline.info/
+
+    // a span to the end of the file
+    size_t b = m_state->pos.offset;
+    substr s = m_buf.sub(b);
+    if(s.begins_with(' '))
+    {
+        s = s.triml(' ');
+        _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.sub(b).is_super(s));
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.begin() >= m_buf.sub(b).begin());
+        _line_progressed((size_t)(s.begin() - m_buf.sub(b).begin()));
+    }
+    b = m_state->pos.offset; // take this into account
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.begins_with('"'));
+
+    // skip the opening quote
+    _line_progressed(1);
+    s = s.sub(1);
+
+    bool needs_filter = false;
+
+    size_t numlines = 1; // we already have one line
+    size_t pos = npos; // find the pos of the matching quote
+    while( ! _finished_file())
+    {
+        const csubstr line = m_state->line_contents.rem;
+        bool line_is_blank = true;
+        _c4dbgpf("scanning double quoted scalar @ line[{}]:  line='{}'", m_state->pos.line, line);
+        for(size_t i = 0; i < line.len; ++i)
+        {
+            const char curr = line.str[i];
+            if(curr != ' ')
+                line_is_blank = false;
+            // every \ is an escape
+            if(curr == '\\')
+            {
+                const char next = i+1 < line.len ? line.str[i+1] : '~';
+                needs_filter = true;
+                if(next == '"' || next == '\\')
+                    ++i;
+            }
+            else if(curr == '"')
+            {
+                pos = i;
+                break;
+            }
+        }
+
+        // leading whitespace also needs filtering
+        needs_filter = needs_filter
+            || (numlines > 1)
+            || line_is_blank
+            || (_at_line_begin() && line.begins_with(' '));
+
+        if(pos == npos)
+        {
+            _line_progressed(line.len);
+            ++numlines;
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, pos >= 0 && pos < m_buf.len);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf[m_state->pos.offset + pos] == '"');
+            _line_progressed(pos + 1); // progress beyond the quote
+            pos = m_state->pos.offset - b - 1; // but we stop before it
+            break;
+        }
+
+        _line_ended();
+        _scan_line();
+    }
+
+    if(pos == npos)
+    {
+        _c4err("reached end of file looking for closing quote");
+    }
+    else
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, pos > 0);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.end() == m_buf.end() || *s.end() == '"');
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.end() >= m_buf.begin() && s.end() <= m_buf.end());
+        s = s.sub(0, pos-1);
+    }
+
+    if(needs_filter)
+    {
+        csubstr ret = _filter_dquot_scalar(s);
+        _c4dbgpf("final scalar: [{}]\"{}\"", ret.len, ret);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, ret.len <= s.len || s.empty() || s.trim(' ').empty());
+        return ret;
+    }
+
+    _c4dbgpf("final scalar: \"{}\"", s);
+
+    return s;
+}
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_scan_block()
+{
+    // nice explanation here: http://yaml-multiline.info/
+    csubstr s = m_state->line_contents.rem;
+    csubstr trimmed = s.triml(' ');
+    if(trimmed.str > s.str)
+    {
+        _c4dbgp("skipping whitespace");
+        _RYML_CB_ASSERT(m_stack.m_callbacks, trimmed.str >= s.str);
+        _line_progressed(static_cast<size_t>(trimmed.str - s.str));
+        s = trimmed;
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.begins_with('|') || s.begins_with('>'));
+
+    _c4dbgpf("scanning block: specs=\"{}\"", s);
+
+    // parse the spec
+    BlockStyle_e newline = s.begins_with('>') ? BLOCK_FOLD : BLOCK_LITERAL;
+    BlockChomp_e chomp = CHOMP_CLIP; // default to clip unless + or - are used
+    size_t indentation = npos; // have to find out if no spec is given
+    csubstr digits;
+    if(s.len > 1)
+    {
+        _RYML_CB_ASSERT(m_stack.m_callbacks, s.begins_with_any("|>"));
+        csubstr t = s.sub(1);
+        _c4dbgpf("scanning block: spec is multichar: '{}'", t);
+        _RYML_CB_ASSERT(m_stack.m_callbacks, t.len >= 1);
+        size_t pos = t.first_of("-+");
+        _c4dbgpf("scanning block: spec chomp char at {}", pos);
+        if(pos != npos)
+        {
+            if(t[pos] == '-')
+                chomp = CHOMP_STRIP;
+            else if(t[pos] == '+')
+                chomp = CHOMP_KEEP;
+            if(pos == 0)
+                t = t.sub(1);
+            else
+                t = t.first(pos);
+        }
+        // from here to the end, only digits are considered
+        digits = t.left_of(t.first_not_of("0123456789"));
+        if( ! digits.empty())
+        {
+            if( ! c4::atou(digits, &indentation))
+                _c4err("parse error: could not read decimal");
+            _c4dbgpf("scanning block: indentation specified: {}. add {} from curr state -> {}", indentation, m_state->indref, indentation+m_state->indref);
+            indentation += m_state->indref;
+        }
+    }
+
+    // finish the current line
+    _line_progressed(s.len);
+    _line_ended();
+    _scan_line();
+
+    _c4dbgpf("scanning block: style={}  chomp={}  indentation={}", newline==BLOCK_FOLD ? "fold" : "literal", chomp==CHOMP_CLIP ? "clip" : (chomp==CHOMP_STRIP ? "strip" : "keep"), indentation);
+
+    // start with a zero-length block, already pointing at the right place
+    substr raw_block(m_buf.data() + m_state->pos.offset, size_t(0));// m_state->line_contents.full.sub(0, 0);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, raw_block.begin() == m_state->line_contents.full.begin());
+
+    // read every full line into a raw block,
+    // from which newlines are to be stripped as needed.
+    //
+    // If no explicit indentation was given, pick it from the first
+    // non-empty line. See
+    // https://yaml.org/spec/1.2.2/#8111-block-indentation-indicator
+    size_t num_lines = 0, first = m_state->pos.line, provisional_indentation = npos;
+    LineContents lc;
+    while(( ! _finished_file()))
+    {
+        // peek next line, but do not advance immediately
+        lc.reset_with_next_line(m_buf, m_state->pos.offset);
+        _c4dbgpf("scanning block: peeking at '{}'", lc.stripped);
+        // evaluate termination conditions
+        if(indentation != npos)
+        {
+            // stop when the line is deindented and not empty
+            if(lc.indentation < indentation && ( ! lc.rem.trim(" \t\r\n").empty()))
+            {
+                _c4dbgpf("scanning block: indentation decreased ref={} thisline={}", indentation, lc.indentation);
+                break;
+            }
+            else if(indentation == 0)
+            {
+                if((lc.rem == "..." || lc.rem.begins_with("... "))
+                    ||
+                   (lc.rem == "---" || lc.rem.begins_with("--- ")))
+                {
+                    _c4dbgp("scanning block: stop. indentation=0 and stream ended");
+                    break;
+                }
+            }
+        }
+        else
+        {
+            _c4dbgpf("scanning block: indentation ref not set. firstnonws={}", lc.stripped.first_not_of(' '));
+            if(lc.stripped.first_not_of(' ') != npos) // non-empty line
+            {
+                _c4dbgpf("scanning block: line not empty. indref={} indprov={} indentation={}", m_state->indref, provisional_indentation, lc.indentation);
+                if(provisional_indentation == npos)
+                {
+                    if(lc.indentation < m_state->indref)
+                    {
+                        _c4dbgpf("scanning block: block terminated indentation={} < indref={}", lc.indentation, m_state->indref);
+                        if(raw_block.len == 0)
+                        {
+                            _c4dbgp("scanning block: was empty, undo next line");
+                            _line_ended_undo();
+                        }
+                        break;
+                    }
+                    else if(lc.indentation == m_state->indref)
+                    {
+                        if(has_any(RSEQ|RMAP))
+                        {
+                            _c4dbgpf("scanning block: block terminated. reading container and indentation={}==indref={}", lc.indentation, m_state->indref);
+                            break;
+                        }
+                    }
+                    _c4dbgpf("scanning block: set indentation ref from this line: ref={}", lc.indentation);
+                    indentation = lc.indentation;
+                }
+                else
+                {
+                    if(lc.indentation >= provisional_indentation)
+                    {
+                        _c4dbgpf("scanning block: set indentation ref from provisional indentation: provisional_ref={}, thisline={}", provisional_indentation, lc.indentation);
+                        //indentation = provisional_indentation ? provisional_indentation : lc.indentation;
+                        indentation = lc.indentation;
+                    }
+                    else
+                    {
+                        break;
+                        //_c4err("parse error: first non-empty block line should have at least the original indentation");
+                    }
+                }
+            }
+            else // empty line
+            {
+                _c4dbgpf("scanning block: line empty or {} spaces. line_indentation={} prov_indentation={}", lc.stripped.len, lc.indentation, provisional_indentation);
+                if(provisional_indentation != npos)
+                {
+                    if(lc.stripped.len >= provisional_indentation)
+                    {
+                        _c4dbgpf("scanning block: increase provisional_ref {} -> {}", provisional_indentation, lc.stripped.len);
+                        provisional_indentation = lc.stripped.len;
+                    }
+                    #ifdef RYML_NO_COVERAGE__TO_BE_DELETED
+                    else if(lc.indentation >= provisional_indentation && lc.indentation != npos)
+                    {
+                        _c4dbgpf("scanning block: increase provisional_ref {} -> {}", provisional_indentation, lc.indentation);
+                        provisional_indentation = lc.indentation;
+                    }
+                    #endif
+                }
+                else
+                {
+                    provisional_indentation = lc.indentation ? lc.indentation : has_any(RSEQ|RVAL);
+                    _c4dbgpf("scanning block: initialize provisional_ref={}", provisional_indentation);
+                    if(provisional_indentation == npos)
+                    {
+                        provisional_indentation = lc.stripped.len ? lc.stripped.len : has_any(RSEQ|RVAL);
+                        _c4dbgpf("scanning block: initialize provisional_ref={}", provisional_indentation);
+                    }
+                }
+            }
+        }
+        // advance now that we know the folded scalar continues
+        m_state->line_contents = lc;
+        _c4dbgpf("scanning block: append '{}'", m_state->line_contents.rem);
+        raw_block.len += m_state->line_contents.full.len;
+        _line_progressed(m_state->line_contents.rem.len);
+        _line_ended();
+        ++num_lines;
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_state->pos.line == (first + num_lines) || (raw_block.len == 0));
+    C4_UNUSED(num_lines);
+    C4_UNUSED(first);
+
+    if(indentation == npos)
+    {
+        _c4dbgpf("scanning block: set indentation from provisional: {}", provisional_indentation);
+        indentation = provisional_indentation;
+    }
+
+    if(num_lines)
+        _line_ended_undo();
+
+    _c4dbgpf("scanning block: raw=~~~{}~~~", raw_block);
+
+    // ok! now we strip the newlines and spaces according to the specs
+    s = _filter_block_scalar(raw_block, newline, chomp, indentation);
+
+    _c4dbgpf("scanning block: final=~~~{}~~~", s);
+
+    return s;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<bool backslash_is_escape, bool keep_trailing_whitespace>
+bool Parser::_filter_nl(substr r, size_t *C4_RESTRICT i, size_t *C4_RESTRICT pos, size_t indentation)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfnl(fmt, ...) _c4dbgpf("filter_nl[{}]: " fmt, *i, __VA_ARGS__)
+    #else
+    #define _c4dbgfnl(...)
+    #endif
+
+    const char curr = r[*i];
+    bool replaced = false;
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, indentation != npos);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, curr == '\n');
+
+    _c4dbgfnl("found newline. sofar=[{}]~~~{}~~~", *pos, m_filter_arena.first(*pos));
+    size_t ii = *i;
+    size_t numnl_following = count_following_newlines(r, &ii, indentation);
+    if(numnl_following)
+    {
+        _c4dbgfnl("{} consecutive (empty) lines {} in the middle. totalws={}", 1+numnl_following, ii < r.len ? "in the middle" : "at the end", ii - *i);
+        for(size_t j = 0; j < numnl_following; ++j)
+            m_filter_arena.str[(*pos)++] = '\n';
+    }
+    else
+    {
+        if(r.first_not_of(" \t", *i+1) != npos)
+        {
+            m_filter_arena.str[(*pos)++] = ' ';
+            _c4dbgfnl("single newline. convert to space. ii={}/{}. sofar=[{}]~~~{}~~~", ii, r.len, *pos, m_filter_arena.first(*pos));
+            replaced = true;
+        }
+        else
+        {
+            if C4_IF_CONSTEXPR (keep_trailing_whitespace)
+            {
+                m_filter_arena.str[(*pos)++] = ' ';
+                _c4dbgfnl("single newline. convert to space. ii={}/{}. sofar=[{}]~~~{}~~~", ii, r.len, *pos, m_filter_arena.first(*pos));
+                replaced = true;
+            }
+            else
+            {
+                _c4dbgfnl("last newline, everything else is whitespace. ii={}/{}", ii, r.len);
+                *i = r.len;
+            }
+        }
+        if C4_IF_CONSTEXPR (backslash_is_escape)
+        {
+            if(ii < r.len && r.str[ii] == '\\')
+            {
+                const char next = ii+1 < r.len ? r.str[ii+1] : '\0';
+                if(next == ' ' || next == '\t')
+                {
+                    _c4dbgfnl("extend skip to backslash{}", "");
+                    ++ii;
+                }
+            }
+        }
+    }
+    *i = ii - 1; // correct for the loop increment
+
+    #undef _c4dbgfnl
+
+    return replaced;
+}
+
+
+//-----------------------------------------------------------------------------
+
+template<bool keep_trailing_whitespace>
+void Parser::_filter_ws(substr r, size_t *C4_RESTRICT i, size_t *C4_RESTRICT pos)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfws(fmt, ...) _c4dbgpf("filt_nl[{}]: " fmt, *i, __VA_ARGS__)
+    #else
+    #define _c4dbgfws(...)
+    #endif
+
+    const char curr = r[*i];
+    _c4dbgfws("found whitespace '{}'", _c4prc(curr));
+    _RYML_CB_ASSERT(m_stack.m_callbacks, curr == ' ' || curr == '\t');
+
+    size_t first = *i > 0 ? r.first_not_of(" \t", *i) : r.first_not_of(' ', *i);
+    if(first != npos)
+    {
+        if(r[first] == '\n' || r[first] == '\r') // skip trailing whitespace
+        {
+            _c4dbgfws("whitespace is trailing on line. firstnonws='{}'@{}", _c4prc(r[first]), first);
+            *i = first - 1; // correct for the loop increment
+        }
+        else // a legit whitespace
+        {
+            m_filter_arena.str[(*pos)++] = curr;
+            _c4dbgfws("legit whitespace. sofar=[{}]~~~{}~~~", *pos, m_filter_arena.first(*pos));
+        }
+    }
+    else
+    {
+        _c4dbgfws("... everything else is trailing whitespace{}", "");
+        if C4_IF_CONSTEXPR (keep_trailing_whitespace)
+            for(size_t j = *i; j < r.len; ++j)
+                m_filter_arena.str[(*pos)++] = r[j];
+        *i = r.len;
+    }
+
+    #undef _c4dbgfws
+}
+
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_filter_plain_scalar(substr s, size_t indentation)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfps(...) _c4dbgpf("filt_plain_scalar" __VA_ARGS__)
+    #else
+    #define _c4dbgfps(...)
+    #endif
+
+    _c4dbgfps("before=~~~{}~~~", s);
+
+    substr r = s.triml(" \t");
+    _grow_filter_arena(r.len);
+    size_t pos = 0; // the filtered size
+    bool filtered_chars = false;
+    for(size_t i = 0; i < r.len; ++i)
+    {
+        const char curr = r.str[i];
+        _c4dbgfps("[{}]: '{}'", i, _c4prc(curr));
+        if(curr == ' ' || curr == '\t')
+        {
+            _filter_ws</*keep_trailing_ws*/false>(r, &i, &pos);
+        }
+        else if(curr == '\n')
+        {
+            filtered_chars = _filter_nl</*backslash_is_escape*/false, /*keep_trailing_ws*/false>(r, &i, &pos, indentation);
+        }
+        else if(curr == '\r')  // skip \r --- https://stackoverflow.com/questions/1885900
+        {
+            ;
+        }
+        else
+        {
+            m_filter_arena.str[pos++] = r[i];
+        }
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+    if(pos < r.len || filtered_chars)
+    {
+        r = _finish_filter_arena(r, pos);
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.len >= r.len);
+    _c4dbgfps("#filteredchars={} after=~~~{}~~~", s.len - r.len, r);
+
+    #undef _c4dbgfps
+    return r;
+}
+
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_filter_squot_scalar(substr s)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfsq(...) _c4dbgpf("filt_squo_scalar")
+    #else
+    #define _c4dbgfsq(...)
+    #endif
+
+    // from the YAML spec for double-quoted scalars:
+    // https://yaml.org/spec/1.2-old/spec.html#style/flow/single-quoted
+
+    _c4dbgfsq(": before=~~~{}~~~", s);
+
+    _grow_filter_arena(s.len);
+    substr r = s;
+    size_t pos = 0; // the filtered size
+    bool filtered_chars = false;
+    for(size_t i = 0; i < r.len; ++i)
+    {
+        const char curr = r[i];
+        _c4dbgfsq("[{}]: '{}'", i, _c4prc(curr));
+        if(curr == ' ' || curr == '\t')
+        {
+            _filter_ws</*keep_trailing_ws*/true>(r, &i, &pos);
+        }
+        else if(curr == '\n')
+        {
+            filtered_chars = _filter_nl</*backslash_is_escape*/false, /*keep_trailing_ws*/true>(r, &i, &pos, /*indentation*/0);
+        }
+        else if(curr == '\r')  // skip \r --- https://stackoverflow.com/questions/1885900
+        {
+            ;
+        }
+        else if(curr == '\'')
+        {
+            char next = i+1 < r.len ? r[i+1] : '\0';
+            if(next == '\'')
+            {
+                _c4dbgfsq("[{}]: two consecutive quotes", i);
+                filtered_chars = true;
+                m_filter_arena.str[pos++] = '\'';
+                ++i;
+            }
+        }
+        else
+        {
+            m_filter_arena.str[pos++] = curr;
+        }
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+    if(pos < r.len || filtered_chars)
+    {
+        r = _finish_filter_arena(r, pos);
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.len >= r.len);
+    _c4dbgpf(": #filteredchars={} after=~~~{}~~~", s.len - r.len, r);
+
+    #undef _c4dbgfsq
+    return r;
+}
+
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_filter_dquot_scalar(substr s)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfdq(...) _c4dbgpf("filt_dquo_scalar" __VA_ARGS__)
+    #else
+    #define _c4dbgfdq(...)
+    #endif
+
+    _c4dbgfdq(": before=~~~{}~~~", s);
+
+    // from the YAML spec for double-quoted scalars:
+    // https://yaml.org/spec/1.2-old/spec.html#style/flow/double-quoted
+    //
+    // All leading and trailing white space characters are excluded
+    // from the content. Each continuation line must therefore contain
+    // at least one non-space character. Empty lines, if any, are
+    // consumed as part of the line folding.
+
+    _grow_filter_arena(s.len + 2u * s.count('\\'));
+    substr r = s;
+    size_t pos = 0; // the filtered size
+    bool filtered_chars = false;
+    for(size_t i = 0; i < r.len; ++i)
+    {
+        const char curr = r[i];
+        _c4dbgfdq("[{}]: '{}'", i, _c4prc(curr));
+        if(curr == ' ' || curr == '\t')
+        {
+            _filter_ws</*keep_trailing_ws*/true>(r, &i, &pos);
+        }
+        else if(curr == '\n')
+        {
+            filtered_chars = _filter_nl</*backslash_is_escape*/true, /*keep_trailing_ws*/true>(r, &i, &pos, /*indentation*/0);
+        }
+        else if(curr == '\r')  // skip \r --- https://stackoverflow.com/questions/1885900
+        {
+            ;
+        }
+        else if(curr == '\\')
+        {
+            char next = i+1 < r.len ? r[i+1] : '\0';
+            _c4dbgfdq("[{}]: backslash, next='{}'", i, _c4prc(next));
+            filtered_chars = true;
+            if(next == '\r')
+            {
+                if(i+2 < r.len && r[i+2] == '\n')
+                {
+                    ++i; // newline escaped with \ -- skip both (add only one as i is loop-incremented)
+                    next = '\n';
+                    _c4dbgfdq("[{}]: was \\r\\n, now next='\\n'", i);
+                }
+            }
+            // remember the loop will also increment i
+            if(next == '\n')
+            {
+                size_t ii = i + 2;
+                for( ; ii < r.len; ++ii)
+                {
+                    if(r.str[ii] == ' ' || r.str[ii] == '\t')  // skip leading whitespace
+                        ;
+                    else
+                        break;
+                }
+                i += ii - i - 1;
+            }
+            else if(next == '"' || next == '/'  || next == ' ' || next == '\t') // escapes for json compatibility
+            {
+                m_filter_arena.str[pos++] = next;
+                ++i;
+            }
+            else if(next == '\r')
+            {
+                //++i;
+            }
+            else if(next == 'n')
+            {
+                m_filter_arena.str[pos++] = '\n';
+                ++i;
+            }
+            else if(next == 'r')
+            {
+                m_filter_arena.str[pos++] = '\r';
+                ++i; // skip
+            }
+            else if(next == 't')
+            {
+                m_filter_arena.str[pos++] = '\t';
+                ++i;
+            }
+            else if(next == '\\')
+            {
+                m_filter_arena.str[pos++] = '\\';
+                ++i;
+            }
+            else if(next == 'x') // UTF8
+            {
+                if(i + 1u + 2u >= r.len)
+                    _c4err("\\x requires 2 hex digits");
+                uint8_t byteval = {};
+                if(!read_hex(r.sub(i + 2u, 2u), &byteval))
+                    _c4err("failed to read \\x codepoint");
+                m_filter_arena.str[pos++] = *(char*)&byteval;
+                i += 1u + 2u;
+            }
+            else if(next == 'u') // UTF16
+            {
+                if(i + 1u + 4u >= r.len)
+                    _c4err("\\u requires 4 hex digits");
+                char readbuf[8];
+                csubstr codepoint = r.sub(i + 2u, 4u);
+                uint32_t codepoint_val = {};
+                if(!read_hex(codepoint, &codepoint_val))
+                    _c4err("failed to parse \\u codepoint");
+                size_t numbytes = decode_code_point((uint8_t*)readbuf, sizeof(readbuf), codepoint_val);
+                C4_ASSERT(numbytes <= 4);
+                memcpy(m_filter_arena.str + pos, readbuf, numbytes);
+                pos += numbytes;
+                i += 1u + 4u;
+            }
+            else if(next == 'U') // UTF32
+            {
+                if(i + 1u + 8u >= r.len)
+                    _c4err("\\U requires 8 hex digits");
+                char readbuf[8];
+                csubstr codepoint = r.sub(i + 2u, 8u);
+                uint32_t codepoint_val = {};
+                if(!read_hex(codepoint, &codepoint_val))
+                    _c4err("failed to parse \\U codepoint");
+                size_t numbytes = decode_code_point((uint8_t*)readbuf, sizeof(readbuf), codepoint_val);
+                C4_ASSERT(numbytes <= 4);
+                memcpy(m_filter_arena.str + pos, readbuf, numbytes);
+                pos += numbytes;
+                i += 1u + 8u;
+            }
+            // https://yaml.org/spec/1.2.2/#rule-c-ns-esc-char
+            else if(next == '0')
+            {
+                m_filter_arena.str[pos++] = '\0';
+                ++i;
+            }
+            else if(next == 'b') // backspace
+            {
+                m_filter_arena.str[pos++] = '\b';
+                ++i;
+            }
+            else if(next == 'f') // form feed
+            {
+                m_filter_arena.str[pos++] = '\f';
+                ++i;
+            }
+            else if(next == 'a') // bell character
+            {
+                m_filter_arena.str[pos++] = '\a';
+                ++i;
+            }
+            else if(next == 'v') // vertical tab
+            {
+                m_filter_arena.str[pos++] = '\v';
+                ++i;
+            }
+            else if(next == 'e') // escape character
+            {
+                m_filter_arena.str[pos++] = '\x1b';
+                ++i;
+            }
+            else if(next == '_') // unicode non breaking space \u00a0
+            {
+                // https://www.compart.com/en/unicode/U+00a0
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x3e, 0xc2);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x60, 0xa0);
+                ++i;
+            }
+            else if(next == 'N') // unicode next line \u0085
+            {
+                // https://www.compart.com/en/unicode/U+0085
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x3e, 0xc2);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x7b, 0x85);
+                ++i;
+            }
+            else if(next == 'L') // unicode line separator \u2028
+            {
+                // https://www.utf8-chartable.de/unicode-utf8-table.pl?start=8192&number=1024&names=-&utf8=0x&unicodeinhtml=hex
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x1e, 0xe2);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x80, 0x80);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x58, 0xa8);
+                ++i;
+            }
+            else if(next == 'P') // unicode paragraph separator \u2029
+            {
+                // https://www.utf8-chartable.de/unicode-utf8-table.pl?start=8192&number=1024&names=-&utf8=0x&unicodeinhtml=hex
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x1e, 0xe2);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x80, 0x80);
+                m_filter_arena.str[pos++] = _RYML_CHCONST(-0x57, 0xa9);
+                ++i;
+            }
+            _c4dbgfdq("[{}]: backslash...sofar=[{}]~~~{}~~~", i, pos, m_filter_arena.first(pos));
+        }
+        else
+        {
+            m_filter_arena.str[pos++] = curr;
+        }
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+    if(pos < r.len || filtered_chars)
+    {
+        r = _finish_filter_arena(r, pos);
+    }
+
+    _RYML_CB_ASSERT(m_stack.m_callbacks, s.len >= r.len);
+    _c4dbgpf(": #filteredchars={} after=~~~{}~~~", s.len - r.len, r);
+
+    #undef _c4dbgfdq
+
+    return r;
+}
+
+
+//-----------------------------------------------------------------------------
+bool Parser::_apply_chomp(substr buf, size_t *C4_RESTRICT pos, BlockChomp_e chomp)
+{
+    substr trimmed = buf.first(*pos).trimr('\n');
+    bool added_newline = false;
+    switch(chomp)
+    {
+    case CHOMP_KEEP:
+        if(trimmed.len == *pos)
+        {
+            _c4dbgpf("chomp=KEEP: add missing newline @{}", *pos);
+            //m_filter_arena.str[(*pos)++] = '\n';
+            added_newline = true;
+        }
+        break;
+    case CHOMP_CLIP:
+        if(trimmed.len == *pos)
+        {
+            _c4dbgpf("chomp=CLIP: add missing newline @{}", *pos);
+            m_filter_arena.str[(*pos)++] = '\n';
+            added_newline = true;
+        }
+        else
+        {
+            _c4dbgpf("chomp=CLIP: include single trailing newline @{}", trimmed.len+1);
+            *pos = trimmed.len + 1;
+        }
+        break;
+    case CHOMP_STRIP:
+        _c4dbgpf("chomp=STRIP: strip {}-{}-{} newlines", *pos, trimmed.len, *pos-trimmed.len);
+        *pos = trimmed.len;
+        break;
+    default:
+        _c4err("unknown chomp style");
+    }
+    return added_newline;
+}
+
+
+//-----------------------------------------------------------------------------
+csubstr Parser::_filter_block_scalar(substr s, BlockStyle_e style, BlockChomp_e chomp, size_t indentation)
+{
+    // a debugging scaffold:
+    #if 0
+    #define _c4dbgfbl(fmt, ...) _c4dbgpf("filt_block" fmt, __VA_ARGS__)
+    #else
+    #define _c4dbgfbl(...)
+    #endif
+
+    _c4dbgfbl(": indentation={} before=[{}]~~~{}~~~", indentation, s.len, s);
+
+    if(chomp != CHOMP_KEEP && s.trim(" \n\r").len == 0u)
+    {
+        _c4dbgp("filt_block: empty scalar");
+        return s.first(0);
+    }
+
+    substr r = s;
+
+    switch(style)
+    {
+    case BLOCK_LITERAL:
+        {
+            _c4dbgp("filt_block: style=literal");
+            // trim leading whitespace up to indentation
+            {
+                size_t numws = r.first_not_of(' ');
+                if(numws != npos)
+                {
+                    if(numws > indentation)
+                        r = r.sub(indentation);
+                    else
+                        r = r.sub(numws);
+                    _c4dbgfbl(": after triml=[{}]~~~{}~~~", r.len, r);
+                }
+                else
+                {
+                    if(chomp != CHOMP_KEEP || r.len == 0)
+                    {
+                        _c4dbgfbl(": all spaces {}, return empty", r.len);
+                        return r.first(0);
+                    }
+                    else
+                    {
+                        r[0] = '\n';
+                        return r.first(1);
+                    }
+                }
+            }
+            _grow_filter_arena(s.len + 2u);  // use s.len! because we may need to add a newline at the end, so the leading indentation will allow space for that newline
+            size_t pos = 0; // the filtered size
+            for(size_t i = 0; i < r.len; ++i)
+            {
+                const char curr = r.str[i];
+                _c4dbgfbl("[{}]='{}'  pos={}", i, _c4prc(curr), pos);
+                if(curr == '\r')
+                    continue;
+                m_filter_arena.str[pos++] = curr;
+                if(curr == '\n')
+                {
+                    _c4dbgfbl("[{}]: found newline", i);
+                    // skip indentation on the next line
+                    csubstr rem = r.sub(i+1);
+                    size_t first = rem.first_not_of(' ');
+                    if(first != npos)
+                    {
+                        _RYML_CB_ASSERT(m_stack.m_callbacks, first < rem.len);
+                        _RYML_CB_ASSERT(m_stack.m_callbacks, i+1+first < r.len);
+                        _c4dbgfbl("[{}]: {} spaces follow before next nonws character @ [{}]='{}'", i, first, i+1+first, rem.str[first]);
+                        if(first < indentation)
+                        {
+                            _c4dbgfbl("[{}]: skip {}<{} spaces from indentation", i, first, indentation);
+                            i += first;
+                        }
+                        else
+                        {
+                            _c4dbgfbl("[{}]: skip {} spaces from indentation", i, indentation);
+                            i += indentation;
+                        }
+                    }
+                    else
+                    {
+                        _RYML_CB_ASSERT(m_stack.m_callbacks, i+1 <= r.len);
+                        first = rem.len;
+                        _c4dbgfbl("[{}]: {} spaces to the end", i, first);
+                        if(first)
+                        {
+                            if(first < indentation)
+                            {
+                                _c4dbgfbl("[{}]: skip everything", i);
+                                --pos;
+                                break;
+                            }
+                            else
+                            {
+                                _c4dbgfbl("[{}]: skip {} spaces from indentation", i, indentation);
+                                i += indentation;
+                            }
+                        }
+                        else if(i+1 == r.len)
+                        {
+                            if(chomp == CHOMP_STRIP)
+                                --pos;
+                            break;
+                        }
+                    }
+                }
+            }
+            _RYML_CB_ASSERT(m_stack.m_callbacks, s.len >= pos);
+            _c4dbgfbl(": #filteredchars={} after=~~~{}~~~", s.len - r.len, r);
+            bool changed = _apply_chomp(m_filter_arena, &pos, chomp);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+            _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= s.len);
+            if(pos < r.len || changed)
+            {
+                r = _finish_filter_arena(s, pos); // write into s
+            }
+            break;
+        }
+    case BLOCK_FOLD:
+        {
+            _c4dbgp("filt_block: style=fold");
+            _grow_filter_arena(r.len + 2);
+            size_t pos = 0; // the filtered size
+            bool filtered_chars = false;
+            bool started = false;
+            bool is_indented = false;
+            size_t i = r.first_not_of(' ');
+            _c4dbgfbl(": first non space at {}", i);
+            if(i > indentation)
+            {
+                is_indented = true;
+                i = indentation;
+            }
+            _c4dbgfbl(": start folding at {}, is_indented={}", i, (int)is_indented);
+            auto on_change_indentation = [&](size_t numnl_following, size_t last_newl, size_t first_non_whitespace){
+                _c4dbgfbl("[{}]: add 1+{} newlines", i, numnl_following);
+                for(size_t j = 0; j < 1 + numnl_following; ++j)
+                    m_filter_arena.str[pos++] = '\n';
+                for(i = last_newl + 1 + indentation; i < first_non_whitespace; ++i)
+                {
+                    if(r.str[i] == '\r')
+                        continue;
+                    _c4dbgfbl("[{}]: add '{}'", i, _c4prc(r.str[i]));
+                    m_filter_arena.str[pos++] = r.str[i];
+                }
+                --i;
+            };
+            for( ; i < r.len; ++i)
+            {
+                const char curr = r.str[i];
+                _c4dbgfbl("[{}]='{}'", i, _c4prc(curr));
+                if(curr == '\n')
+                {
+                    filtered_chars = true;
+                    // skip indentation on the next line, and advance over the next non-indented blank lines as well
+                    size_t first_non_whitespace;
+                    size_t numnl_following = (size_t)-1;
+                    while(r[i] == '\n')
+                    {
+                        ++numnl_following;
+                        csubstr rem = r.sub(i+1);
+                        size_t first = rem.first_not_of(' ');
+                        _c4dbgfbl("[{}]: found newline. first={} rem.len={}", i, first, rem.len);
+                        if(first != npos)
+                        {
+                            first_non_whitespace = first + i+1;
+                            while(first_non_whitespace < r.len && r[first_non_whitespace] == '\r')
+                                ++first_non_whitespace;
+                            _RYML_CB_ASSERT(m_stack.m_callbacks, first < rem.len);
+                            _RYML_CB_ASSERT(m_stack.m_callbacks, i+1+first < r.len);
+                            _c4dbgfbl("[{}]: {} spaces follow before next nonws character @ [{}]='{}'", i, first, i+1+first, _c4prc(rem.str[first]));
+                            if(first < indentation)
+                            {
+                                _c4dbgfbl("[{}]: skip {}<{} spaces from indentation", i, first, indentation);
+                                i += first;
+                            }
+                            else
+                            {
+                                _c4dbgfbl("[{}]: skip {} spaces from indentation", i, indentation);
+                                i += indentation;
+                                if(first > indentation)
+                                {
+                                    _c4dbgfbl("[{}]: {} further indented than {}, stop newlining", i, first, indentation);
+                                    goto finished_counting_newlines;
+                                }
+                            }
+                            // prepare the next while loop iteration
+                            // by setting i at the next newline after
+                            // an empty line
+                            if(r[first_non_whitespace] == '\n')
+                                i = first_non_whitespace;
+                            else
+                                goto finished_counting_newlines;
+                        }
+                        else
+                        {
+                            _RYML_CB_ASSERT(m_stack.m_callbacks, i+1 <= r.len);
+                            first = rem.len;
+                            first_non_whitespace = first + i+1;
+                            if(first)
+                            {
+                                _c4dbgfbl("[{}]: {} spaces to the end", i, first);
+                                if(first < indentation)
+                                {
+                                    _c4dbgfbl("[{}]: skip everything", i);
+                                    i += first;
+                                }
+                                else
+                                {
+                                    _c4dbgfbl("[{}]: skip {} spaces from indentation", i, indentation);
+                                    i += indentation;
+                                    if(first > indentation)
+                                    {
+                                        _c4dbgfbl("[{}]: {} spaces missing. not done yet", i, indentation - first);
+                                        goto finished_counting_newlines;
+                                    }
+                                }
+                            }
+                            else // if(i+1 == r.len)
+                            {
+                                _c4dbgfbl("[{}]: it's the final newline", i);
+                                _RYML_CB_ASSERT(m_stack.m_callbacks, i+1 == r.len);
+                                _RYML_CB_ASSERT(m_stack.m_callbacks, rem.len == 0);
+                            }
+                            goto end_of_scalar;
+                        }
+                    }
+                end_of_scalar:
+                    // Write all the trailing newlines. Since we're
+                    // at the end no folding is needed, so write every
+                    // newline (add 1).
+                    _c4dbgfbl("[{}]: add {} trailing newlines", i, 1+numnl_following);
+                    for(size_t j = 0; j < 1 + numnl_following; ++j)
+                        m_filter_arena.str[pos++] = '\n';
+                    break;
+                finished_counting_newlines:
+                    _c4dbgfbl("[{}]: #newlines={} firstnonws={}", i, numnl_following, first_non_whitespace);
+                    while(first_non_whitespace < r.len && r[first_non_whitespace] == '\t')
+                        ++first_non_whitespace;
+                    _c4dbgfbl("[{}]: #newlines={} firstnonws={}", i, numnl_following, first_non_whitespace);
+                    _RYML_CB_ASSERT(m_stack.m_callbacks, first_non_whitespace <= r.len);
+                    size_t last_newl = r.last_of('\n', first_non_whitespace);
+                    size_t this_indentation = first_non_whitespace - last_newl - 1;
+                    _c4dbgfbl("[{}]: #newlines={} firstnonws={} lastnewl={} this_indentation={} vs indentation={}", i, numnl_following, first_non_whitespace, last_newl, this_indentation, indentation);
+                    _RYML_CB_ASSERT(m_stack.m_callbacks, first_non_whitespace >= last_newl + 1);
+                    _RYML_CB_ASSERT(m_stack.m_callbacks, this_indentation >= indentation);
+                    if(!started)
+                    {
+                        _c4dbgfbl("[{}]: #newlines={}. write all leading newlines", i, numnl_following);
+                        for(size_t j = 0; j < 1 + numnl_following; ++j)
+                            m_filter_arena.str[pos++] = '\n';
+                        if(this_indentation > indentation)
+                        {
+                            is_indented = true;
+                            _c4dbgfbl("[{}]: advance ->{}", i, last_newl + indentation);
+                            i = last_newl + indentation;
+                        }
+                        else
+                        {
+                            i = first_non_whitespace - 1;
+                            _c4dbgfbl("[{}]: advance ->{}", i, first_non_whitespace);
+                        }
+                    }
+                    else if(this_indentation == indentation)
+                    {
+                        _c4dbgfbl("[{}]: same indentation", i);
+                        if(!is_indented)
+                        {
+                            if(numnl_following == 0)
+                            {
+                                _c4dbgfbl("[{}]: fold!", i);
+                                m_filter_arena.str[pos++] = ' ';
+                            }
+                            else
+                            {
+                                _c4dbgfbl("[{}]: add {} newlines", i, 1 + numnl_following);
+                                for(size_t j = 0; j < numnl_following; ++j)
+                                    m_filter_arena.str[pos++] = '\n';
+                            }
+                            i = first_non_whitespace - 1;
+                            _c4dbgfbl("[{}]: advance {}->{}", i, i, first_non_whitespace);
+                        }
+                        else
+                        {
+                            _c4dbgfbl("[{}]: back to ref indentation", i);
+                            is_indented = false;
+                            on_change_indentation(numnl_following, last_newl, first_non_whitespace);
+                            _c4dbgfbl("[{}]: advance {}->{}", i, i, first_non_whitespace);
+                        }
+                    }
+                    else
+                    {
+                        _c4dbgfbl("[{}]: increased indentation.", i);
+                        is_indented = true;
+                        _RYML_CB_ASSERT(m_stack.m_callbacks, this_indentation > indentation);
+                        on_change_indentation(numnl_following, last_newl, first_non_whitespace);
+                        _c4dbgfbl("[{}]: advance {}->{}", i, i, first_non_whitespace);
+                    }
+                }
+                else if(curr != '\r')
+                {
+                    if(curr != '\t')
+                        started = true;
+                    m_filter_arena.str[pos++] = curr;
+                }
+            }
+            _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+            _c4dbgfbl(": #filteredchars={} after=[{}]~~~{}~~~", (int)s.len - (int)pos, pos, m_filter_arena.first(pos));
+            bool changed = _apply_chomp(m_filter_arena, &pos, chomp);
+            if(pos < r.len || filtered_chars || changed)
+            {
+                r = _finish_filter_arena(s, pos); // write into s
+            }
+        }
+        break;
+    default:
+        _c4err("unknown block style");
+    }
+
+    _c4dbgfbl(": final=[{}]~~~{}~~~", r.len, r);
+
+    #undef _c4dbgfbl
+
+    return r;
+}
+
+//-----------------------------------------------------------------------------
+size_t Parser::_count_nlines(csubstr src)
+{
+    return 1 + src.count('\n');
+}
+
+//-----------------------------------------------------------------------------
+void Parser::_handle_directive(csubstr directive_)
+{
+    csubstr directive = directive_;
+    if(directive.begins_with("%TAG"))
+    {
+        TagDirective td;
+        _c4dbgpf("%TAG directive: {}", directive_);
+        directive = directive.sub(4);
+        if(!directive.begins_with(' '))
+            _c4err("malformed tag directive: {}", directive_);
+        directive = directive.triml(' ');
+        size_t pos = directive.find(' ');
+        if(pos == npos)
+            _c4err("malformed tag directive: {}", directive_);
+        td.handle = directive.first(pos);
+        directive = directive.sub(td.handle.len).triml(' ');
+        pos = directive.find(' ');
+        if(pos != npos)
+            directive = directive.first(pos);
+        td.prefix = directive;
+        td.next_node_id = m_tree->size();
+        if(m_tree->size() > 0)
+        {
+            size_t prev = m_tree->size() - 1;
+            if(m_tree->is_root(prev) && m_tree->type(prev) != NOTYPE && !m_tree->is_stream(prev))
+                ++td.next_node_id;
+        }
+        _c4dbgpf("%TAG: handle={} prefix={} next_node={}", td.handle, td.prefix, td.next_node_id);
+        m_tree->add_tag_directive(td);
+    }
+    else if(directive.begins_with("%YAML"))
+    {
+        _c4dbgpf("%YAML directive! ignoring...: {}", directive);
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Parser::set_flags(flag_t f, State * s)
+{
+#ifdef RYML_DBG
+    char buf1_[64], buf2_[64];
+    csubstr buf1 = _prfl(buf1_, f);
+    csubstr buf2 = _prfl(buf2_, s->flags);
+    _c4dbgpf("state[{}]: setting flags to {}: before={}", s-m_stack.begin(), buf1, buf2);
+#endif
+    s->flags = f;
+}
+
+void Parser::add_flags(flag_t on, State * s)
+{
+#ifdef RYML_DBG
+    char buf1_[64], buf2_[64], buf3_[64];
+    csubstr buf1 = _prfl(buf1_, on);
+    csubstr buf2 = _prfl(buf2_, s->flags);
+    csubstr buf3 = _prfl(buf3_, s->flags|on);
+    _c4dbgpf("state[{}]: adding flags {}: before={} after={}", s-m_stack.begin(), buf1, buf2, buf3);
+#endif
+    s->flags |= on;
+}
+
+void Parser::addrem_flags(flag_t on, flag_t off, State * s)
+{
+#ifdef RYML_DBG
+    char buf1_[64], buf2_[64], buf3_[64], buf4_[64];
+    csubstr buf1 = _prfl(buf1_, on);
+    csubstr buf2 = _prfl(buf2_, off);
+    csubstr buf3 = _prfl(buf3_, s->flags);
+    csubstr buf4 = _prfl(buf4_, ((s->flags|on)&(~off)));
+    _c4dbgpf("state[{}]: adding flags {} / removing flags {}: before={} after={}", s-m_stack.begin(), buf1, buf2, buf3, buf4);
+#endif
+    s->flags |= on;
+    s->flags &= ~off;
+}
+
+void Parser::rem_flags(flag_t off, State * s)
+{
+#ifdef RYML_DBG
+    char buf1_[64], buf2_[64], buf3_[64];
+    csubstr buf1 = _prfl(buf1_, off);
+    csubstr buf2 = _prfl(buf2_, s->flags);
+    csubstr buf3 = _prfl(buf3_, s->flags&(~off));
+    _c4dbgpf("state[{}]: removing flags {}: before={} after={}", s-m_stack.begin(), buf1, buf2, buf3);
+#endif
+    s->flags &= ~off;
+}
+
+//-----------------------------------------------------------------------------
+
+csubstr Parser::_prfl(substr buf, flag_t flags)
+{
+    size_t pos = 0;
+    bool gotone = false;
+
+    #define _prflag(fl)                                     \
+    if((flags & fl) == (fl))                                \
+    {                                                       \
+        if(gotone)                                          \
+        {                                                   \
+            if(pos + 1 < buf.len)                           \
+                buf[pos] = '|';                             \
+            ++pos;                                          \
+        }                                                   \
+        csubstr fltxt = #fl;                                \
+        if(pos + fltxt.len <= buf.len)                      \
+            memcpy(buf.str + pos, fltxt.str, fltxt.len);    \
+        pos += fltxt.len;                                   \
+        gotone = true;                                      \
+    }
+
+    _prflag(RTOP);
+    _prflag(RUNK);
+    _prflag(RMAP);
+    _prflag(RSEQ);
+    _prflag(FLOW);
+    _prflag(QMRK);
+    _prflag(RKEY);
+    _prflag(RVAL);
+    _prflag(RNXT);
+    _prflag(SSCL);
+    _prflag(QSCL);
+    _prflag(RSET);
+    _prflag(NDOC);
+    _prflag(RSEQIMAP);
+
+    #undef _prflag
+
+    RYML_ASSERT(pos <= buf.len);
+
+    return buf.first(pos);
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+void Parser::_grow_filter_arena(size_t num_characters_needed)
+{
+    _c4dbgpf("grow: arena={} numchars={}", m_filter_arena.len, num_characters_needed);
+    if(num_characters_needed <= m_filter_arena.len)
+        return;
+    size_t sz = m_filter_arena.len << 1;
+    _c4dbgpf("grow: sz={}", sz);
+    sz = num_characters_needed > sz ? num_characters_needed : sz;
+    _c4dbgpf("grow: sz={}", sz);
+    sz = sz < 128u ? 128u : sz;
+    _c4dbgpf("grow: sz={}", sz);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, sz >= num_characters_needed);
+    _resize_filter_arena(sz);
+}
+
+void Parser::_resize_filter_arena(size_t num_characters)
+{
+    if(num_characters > m_filter_arena.len)
+    {
+        _c4dbgpf("resize: sz={}", num_characters);
+        char *prev = m_filter_arena.str;
+        if(m_filter_arena.str)
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_filter_arena.len > 0);
+            _RYML_CB_FREE(m_stack.m_callbacks, m_filter_arena.str, char, m_filter_arena.len);
+        }
+        m_filter_arena.str = _RYML_CB_ALLOC_HINT(m_stack.m_callbacks, char, num_characters, prev);
+        m_filter_arena.len = num_characters;
+    }
+}
+
+substr Parser::_finish_filter_arena(substr dst, size_t pos)
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= m_filter_arena.len);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, pos <= dst.len);
+    memcpy(dst.str, m_filter_arena.str, pos);
+    return dst.first(pos);
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+csubstr Parser::location_contents(Location const& loc) const
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, loc.offset < m_buf.len);
+    return m_buf.sub(loc.offset);
+}
+
+Location Parser::location(ConstNodeRef node) const
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, node.valid());
+    return location(*node.tree(), node.id());
+}
+
+Location Parser::location(Tree const& tree, size_t node) const
+{
+    // try hard to avoid getting the location from a null string.
+    Location loc;
+    if(_location_from_node(tree, node, &loc, 0))
+        return loc;
+    return val_location(m_buf.str);
+}
+
+bool Parser::_location_from_node(Tree const& tree, size_t node, Location *C4_RESTRICT loc, size_t level) const
+{
+    if(tree.has_key(node))
+    {
+        csubstr k = tree.key(node);
+        if(C4_LIKELY(k.str != nullptr))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, k.is_sub(m_buf));
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.is_super(k));
+            *loc = val_location(k.str);
+            return true;
+        }
+    }
+
+    if(tree.has_val(node))
+    {
+        csubstr v = tree.val(node);
+        if(C4_LIKELY(v.str != nullptr))
+        {
+            _RYML_CB_ASSERT(m_stack.m_callbacks, v.is_sub(m_buf));
+            _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.is_super(v));
+            *loc = val_location(v.str);
+            return true;
+        }
+    }
+
+    if(tree.is_container(node))
+    {
+        if(_location_from_cont(tree, node, loc))
+            return true;
+    }
+
+    if(tree.type(node) != NOTYPE && level == 0)
+    {
+        // try the prev sibling
+        {
+            const size_t prev = tree.prev_sibling(node);
+            if(prev != NONE)
+            {
+                if(_location_from_node(tree, prev, loc, level+1))
+                    return true;
+            }
+        }
+        // try the next sibling
+        {
+            const size_t next = tree.next_sibling(node);
+            if(next != NONE)
+            {
+                if(_location_from_node(tree, next, loc, level+1))
+                    return true;
+            }
+        }
+        // try the parent
+        {
+            const size_t parent = tree.parent(node);
+            if(parent != NONE)
+            {
+                if(_location_from_node(tree, parent, loc, level+1))
+                    return true;
+            }
+        }
+    }
+
+    return false;
+}
+
+bool Parser::_location_from_cont(Tree const& tree, size_t node, Location *C4_RESTRICT loc) const
+{
+    _RYML_CB_ASSERT(m_stack.m_callbacks, tree.is_container(node));
+    if(!tree.is_stream(node))
+    {
+        const char *node_start = tree._p(node)->m_val.scalar.str;  // this was stored in the container
+        if(tree.has_children(node))
+        {
+            size_t child = tree.first_child(node);
+            if(tree.has_key(child))
+            {
+                // when a map starts, the container was set after the key
+                csubstr k = tree.key(child);
+                if(k.str && node_start > k.str)
+                    node_start = k.str;
+            }
+        }
+        *loc = val_location(node_start);
+        return true;
+    }
+    else // it's a stream
+    {
+        *loc = val_location(m_buf.str); // just return the front of the buffer
+    }
+    return true;
+}
+
+
+Location Parser::val_location(const char *val) const
+{
+    if(C4_UNLIKELY(val == nullptr))
+        return {m_file, 0, 0, 0};
+
+    _RYML_CB_CHECK(m_stack.m_callbacks, m_options.locations());
+    // NOTE: if any of these checks fails, the parser needs to be
+    // instantiated with locations enabled.
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.str == m_newline_offsets_buf.str);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_buf.len == m_newline_offsets_buf.len);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_options.locations());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, !_locations_dirty());
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_newline_offsets != nullptr);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_newline_offsets_size > 0);
+    // NOTE: the pointer needs to belong to the buffer that was used to parse.
+    csubstr src = m_buf;
+    _RYML_CB_CHECK(m_stack.m_callbacks, val != nullptr || src.str == nullptr);
+    _RYML_CB_CHECK(m_stack.m_callbacks, (val >= src.begin() && val <= src.end()) || (src.str == nullptr && val == nullptr));
+    // ok. search the first stored newline after the given ptr
+    using lineptr_type = size_t const* C4_RESTRICT;
+    lineptr_type lineptr = nullptr;
+    size_t offset = (size_t)(val - src.begin());
+    if(m_newline_offsets_size < 30) // TODO magic number
+    {
+        // just do a linear search if the size is small.
+        for(lineptr_type curr = m_newline_offsets, last = m_newline_offsets + m_newline_offsets_size; curr < last; ++curr)
+        {
+            if(*curr > offset)
+            {
+                lineptr = curr;
+                break;
+            }
+        }
+    }
+    else
+    {
+        // do a bisection search if the size is not small.
+        //
+        // We could use std::lower_bound but this is simple enough and
+        // spares the include of <algorithm>.
+        size_t count = m_newline_offsets_size;
+        size_t step;
+        lineptr_type it;
+        lineptr = m_newline_offsets;
+        while(count)
+        {
+            step = count >> 1;
+            it = lineptr + step;
+            if(*it < offset)
+            {
+                lineptr = ++it;
+                count -= step + 1;
+            }
+            else
+            {
+                count = step;
+            }
+        }
+    }
+    _RYML_CB_ASSERT(m_stack.m_callbacks, lineptr >= m_newline_offsets);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, lineptr <= m_newline_offsets + m_newline_offsets_size);
+    _RYML_CB_ASSERT(m_stack.m_callbacks, *lineptr > offset);
+    Location loc;
+    loc.name = m_file;
+    loc.offset = offset;
+    loc.line = (size_t)(lineptr - m_newline_offsets);
+    if(lineptr > m_newline_offsets)
+        loc.col = (offset - *(lineptr-1) - 1u);
+    else
+        loc.col = offset;
+    return loc;
+}
+
+void Parser::_prepare_locations()
+{
+    m_newline_offsets_buf = m_buf;
+    size_t numnewlines = 1u + m_buf.count('\n');
+    _resize_locations(numnewlines);
+    m_newline_offsets_size = 0;
+    for(size_t i = 0; i < m_buf.len; i++)
+        if(m_buf[i] == '\n')
+            m_newline_offsets[m_newline_offsets_size++] = i;
+    m_newline_offsets[m_newline_offsets_size++] = m_buf.len;
+    _RYML_CB_ASSERT(m_stack.m_callbacks, m_newline_offsets_size == numnewlines);
+}
+
+void Parser::_resize_locations(size_t numnewlines)
+{
+    if(numnewlines > m_newline_offsets_capacity)
+    {
+        if(m_newline_offsets)
+            _RYML_CB_FREE(m_stack.m_callbacks, m_newline_offsets, size_t, m_newline_offsets_capacity);
+        m_newline_offsets = _RYML_CB_ALLOC_HINT(m_stack.m_callbacks, size_t, numnewlines, m_newline_offsets);
+        m_newline_offsets_capacity = numnewlines;
+    }
+}
+
+bool Parser::_locations_dirty() const
+{
+    return !m_newline_offsets_size;
+}
+
+} // namespace yml
+} // namespace c4
+
+
+#if defined(_MSC_VER)
+#   pragma warning(pop)
+#elif defined(__clang__)
+#   pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic pop
+#endif
diff --git a/thirdparty/ryml/src/c4/yml/parse.hpp b/thirdparty/ryml/src/c4/yml/parse.hpp
new file mode 100644
index 000000000..659edf7e0
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/parse.hpp
@@ -0,0 +1,706 @@
+#ifndef _C4_YML_PARSE_HPP_
+#define _C4_YML_PARSE_HPP_
+
+#ifndef _C4_YML_TREE_HPP_
+#include "c4/yml/tree.hpp"
+#endif
+
+#ifndef _C4_YML_NODE_HPP_
+#include "c4/yml/node.hpp"
+#endif
+
+#ifndef _C4_YML_DETAIL_STACK_HPP_
+#include "c4/yml/detail/stack.hpp"
+#endif
+
+#include <stdarg.h>
+
+#if defined(_MSC_VER)
+#   pragma warning(push)
+#   pragma warning(disable: 4251/*needs to have dll-interface to be used by clients of struct*/)
+#endif
+
+namespace c4 {
+namespace yml {
+
+struct RYML_EXPORT ParserOptions
+{
+private:
+
+    typedef enum : uint32_t {
+        LOCATIONS = (1 << 0),
+        DEFAULTS = 0,
+    } Flags_e;
+
+    uint32_t flags = DEFAULTS;
+public:
+    ParserOptions() = default;
+
+    /** @name source location tracking */
+    /** @{ */
+
+    /** enable/disable source location tracking */
+    ParserOptions& locations(bool enabled)
+    {
+        if(enabled)
+            flags |= LOCATIONS;
+        else
+            flags &= ~LOCATIONS;
+        return *this;
+    }
+    bool locations() const { return (flags & LOCATIONS) != 0u; }
+
+    /** @} */
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+class RYML_EXPORT Parser
+{
+public:
+
+    /** @name construction and assignment */
+    /** @{ */
+
+    Parser(Callbacks const& cb, ParserOptions opts={});
+    Parser(ParserOptions opts={}) : Parser(get_callbacks(), opts) {}
+    ~Parser();
+
+    Parser(Parser &&);
+    Parser(Parser const&);
+    Parser& operator=(Parser &&);
+    Parser& operator=(Parser const&);
+
+    /** @} */
+
+public:
+
+    /** @name modifiers */
+    /** @{ */
+
+    /** Reserve a certain capacity for the parsing stack.
+     * This should be larger than the expected depth of the parsed
+     * YAML tree.
+     *
+     * The parsing stack is the only (potential) heap memory used by
+     * the parser.
+     *
+     * If the requested capacity is below the default
+     * stack size of 16, the memory is used directly in the parser
+     * object; otherwise it will be allocated from the heap.
+     *
+     * @note this reserves memory only for the parser itself; all the
+     * allocations for the parsed tree will go through the tree's
+     * allocator.
+     *
+     * @note the tree and the arena can (and should) also be reserved. */
+    void reserve_stack(size_t capacity)
+    {
+        m_stack.reserve(capacity);
+    }
+
+    /** Reserve a certain capacity for the array used to track node
+     * locations in the source buffer. */
+    void reserve_locations(size_t num_source_lines)
+    {
+        _resize_locations(num_source_lines);
+    }
+
+    /** Reserve a certain capacity for the character arena used to
+     * filter scalars. */
+    void reserve_filter_arena(size_t num_characters)
+    {
+        _resize_filter_arena(num_characters);
+    }
+
+    /** @} */
+
+public:
+
+    /** @name getters and modifiers */
+    /** @{ */
+
+    /** Get the current callbacks in the parser. */
+    Callbacks callbacks() const { return m_stack.m_callbacks; }
+
+    /** Get the name of the latest file parsed by this object. */
+    csubstr filename() const { return m_file; }
+
+    /** Get the latest YAML buffer parsed by this object. */
+    csubstr source() const { return m_buf; }
+
+    size_t stack_capacity() const { return m_stack.capacity(); }
+    size_t locations_capacity() const { return m_newline_offsets_capacity; }
+    size_t filter_arena_capacity() const { return m_filter_arena.len; }
+
+    ParserOptions const& options() const { return m_options; }
+
+    /** @} */
+
+public:
+
+    /** @name parse_in_place */
+    /** @{ */
+
+    /** Create a new tree and parse into its root.
+     * The tree is created with the callbacks currently in the parser. */
+    Tree parse_in_place(csubstr filename, substr src)
+    {
+        Tree t(callbacks());
+        t.reserve(_estimate_capacity(src));
+        this->parse_in_place(filename, src, &t, t.root_id());
+        return t;
+    }
+
+    /** Parse into an existing tree, starting at its root node.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_place(csubstr filename, substr src, Tree *t)
+    {
+        this->parse_in_place(filename, src, t, t->root_id());
+    }
+
+    /** Parse into an existing node.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_place(csubstr filename, substr src, Tree *t, size_t node_id);
+    //   ^^^^^^^^^^^^^ this is the workhorse overload; everything else is syntactic candy
+
+    /** Parse into an existing node.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_place(csubstr filename, substr src, NodeRef node)
+    {
+        this->parse_in_place(filename, src, node.tree(), node.id());
+    }
+
+    RYML_DEPRECATED("use parse_in_place() instead") Tree parse(csubstr filename, substr src) { return parse_in_place(filename, src); }
+    RYML_DEPRECATED("use parse_in_place() instead") void parse(csubstr filename, substr src, Tree *t) { parse_in_place(filename, src, t); }
+    RYML_DEPRECATED("use parse_in_place() instead") void parse(csubstr filename, substr src, Tree *t, size_t node_id) { parse_in_place(filename, src, t, node_id); }
+    RYML_DEPRECATED("use parse_in_place() instead") void parse(csubstr filename, substr src, NodeRef node) { parse_in_place(filename, src, node); }
+
+    /** @} */
+
+public:
+
+    /** @name parse_in_arena: copy the YAML source buffer to the
+     * tree's arena, then parse the copy in situ
+     *
+     * @note overloads receiving a substr YAML buffer are intentionally
+     * left undefined, such that calling parse_in_arena() with a substr
+     * will cause a linker error. This is to prevent an accidental
+     * copy of the source buffer to the tree's arena, because substr
+     * is implicitly convertible to csubstr. If you really intend to parse
+     * a mutable buffer in the tree's arena, convert it first to immutable
+     * by assigning the substr to a csubstr prior to calling parse_in_arena().
+     * This is not needed for parse_in_place() because csubstr is not
+     * implicitly convertible to substr. */
+    /** @{ */
+
+    // READ THE NOTE ABOVE!
+    #define RYML_DONT_PARSE_SUBSTR_IN_ARENA "Do not pass a (mutable) substr to parse_in_arena(); if you have a substr, it should be parsed in place. Consider using parse_in_place() instead, or convert the buffer to csubstr prior to calling. This function is deliberately left undefined and will cause a linker error."
+    RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) Tree parse_in_arena(csubstr filename, substr csrc);
+    RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr csrc, Tree *t);
+    RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr csrc, Tree *t, size_t node_id);
+    RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr csrc, NodeRef node);
+
+    /** Create a new tree and parse into its root.
+     * The immutable YAML source is first copied to the tree's arena,
+     * and parsed from there.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    Tree parse_in_arena(csubstr filename, csubstr csrc)
+    {
+        Tree t(callbacks());
+        substr src = t.copy_to_arena(csrc);
+        t.reserve(_estimate_capacity(csrc));
+        this->parse_in_place(filename, src, &t, t.root_id());
+        return t;
+    }
+
+    /** Parse into an existing tree, starting at its root node.
+     * The immutable YAML source is first copied to the tree's arena,
+     * and parsed from there.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_arena(csubstr filename, csubstr csrc, Tree *t)
+    {
+        substr src = t->copy_to_arena(csrc);
+        this->parse_in_place(filename, src, t, t->root_id());
+    }
+
+    /** Parse into a specific node in an existing tree.
+     * The immutable YAML source is first copied to the tree's arena,
+     * and parsed from there.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_arena(csubstr filename, csubstr csrc, Tree *t, size_t node_id)
+    {
+        substr src = t->copy_to_arena(csrc);
+        this->parse_in_place(filename, src, t, node_id);
+    }
+
+    /** Parse into a specific node in an existing tree.
+     * The immutable YAML source is first copied to the tree's arena,
+     * and parsed from there.
+     * The callbacks in the tree are kept, and used to allocate
+     * the tree members, if any allocation is required. */
+    void parse_in_arena(csubstr filename, csubstr csrc, NodeRef node)
+    {
+        substr src = node.tree()->copy_to_arena(csrc);
+        this->parse_in_place(filename, src, node.tree(), node.id());
+    }
+
+    RYML_DEPRECATED("use parse_in_arena() instead") Tree parse(csubstr filename, csubstr csrc) { return parse_in_arena(filename, csrc); }
+    RYML_DEPRECATED("use parse_in_arena() instead") void parse(csubstr filename, csubstr csrc, Tree *t) { parse_in_arena(filename, csrc, t); }
+    RYML_DEPRECATED("use parse_in_arena() instead") void parse(csubstr filename, csubstr csrc, Tree *t, size_t node_id) { parse_in_arena(filename, csrc, t, node_id); }
+    RYML_DEPRECATED("use parse_in_arena() instead") void parse(csubstr filename, csubstr csrc, NodeRef node) { parse_in_arena(filename, csrc, node); }
+
+    /** @} */
+
+public:
+
+    /** @name locations */
+    /** @{ */
+
+    /** Get the location of a node of the last tree to be parsed by this parser. */
+    Location location(Tree const& tree, size_t node_id) const;
+    /** Get the location of a node of the last tree to be parsed by this parser. */
+    Location location(ConstNodeRef node) const;
+    /** Get the string starting at a particular location, to the end
+     * of the parsed source buffer. */
+    csubstr location_contents(Location const& loc) const;
+    /** Given a pointer to a buffer position, get the location. @p val
+     * must be pointing to somewhere in the source buffer that was
+     * last parsed by this object. */
+    Location val_location(const char *val) const;
+
+    /** @} */
+
+private:
+
+    typedef enum {
+        BLOCK_LITERAL, //!< keep newlines (|)
+        BLOCK_FOLD     //!< replace newline with single space (>)
+    } BlockStyle_e;
+
+    typedef enum {
+        CHOMP_CLIP,    //!< single newline at end (default)
+        CHOMP_STRIP,   //!< no newline at end     (-)
+        CHOMP_KEEP     //!< all newlines from end (+)
+    } BlockChomp_e;
+
+private:
+
+    using flag_t = int;
+
+    static size_t _estimate_capacity(csubstr src) { size_t c = _count_nlines(src); c = c >= 16 ? c : 16; return c; }
+
+    void  _reset();
+
+    bool  _finished_file() const;
+    bool  _finished_line() const;
+
+    csubstr _peek_next_line(size_t pos=npos) const;
+    bool    _advance_to_peeked();
+    void    _scan_line();
+
+    csubstr _slurp_doc_scalar();
+
+    /**
+     * @param [out] quoted
+     * Will only be written to if this method returns true.
+     * Will be set to true if the scanned scalar was quoted, by '', "", > or |.
+     */
+    bool    _scan_scalar_seq_blck(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted);
+    bool    _scan_scalar_map_blck(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted);
+    bool    _scan_scalar_seq_flow(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted);
+    bool    _scan_scalar_map_flow(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted);
+    bool    _scan_scalar_unk(csubstr *C4_RESTRICT scalar, bool *C4_RESTRICT quoted);
+
+    csubstr _scan_comment();
+    csubstr _scan_squot_scalar();
+    csubstr _scan_dquot_scalar();
+    csubstr _scan_block();
+    substr  _scan_plain_scalar_blck(csubstr currscalar, csubstr peeked_line, size_t indentation);
+    substr  _scan_plain_scalar_flow(csubstr currscalar, csubstr peeked_line);
+    substr  _scan_complex_key(csubstr currscalar, csubstr peeked_line);
+    csubstr _scan_to_next_nonempty_line(size_t indentation);
+    csubstr _extend_scanned_scalar(csubstr currscalar);
+
+    csubstr _filter_squot_scalar(const substr s);
+    csubstr _filter_dquot_scalar(substr s);
+    csubstr _filter_plain_scalar(substr s, size_t indentation);
+    csubstr _filter_block_scalar(substr s, BlockStyle_e style, BlockChomp_e chomp, size_t indentation);
+    template<bool backslash_is_escape, bool keep_trailing_whitespace>
+    bool    _filter_nl(substr scalar, size_t *C4_RESTRICT pos, size_t *C4_RESTRICT filter_arena_pos, size_t indentation);
+    template<bool keep_trailing_whitespace>
+    void    _filter_ws(substr scalar, size_t *C4_RESTRICT pos, size_t *C4_RESTRICT filter_arena_pos);
+    bool    _apply_chomp(substr buf, size_t *C4_RESTRICT pos, BlockChomp_e chomp);
+
+    void  _handle_finished_file();
+    void  _handle_line();
+
+    bool  _handle_indentation();
+
+    bool  _handle_unk();
+    bool  _handle_map_flow();
+    bool  _handle_map_blck();
+    bool  _handle_seq_flow();
+    bool  _handle_seq_blck();
+    bool  _handle_top();
+    bool  _handle_types();
+    bool  _handle_key_anchors_and_refs();
+    bool  _handle_val_anchors_and_refs();
+    void  _move_val_tag_to_key_tag();
+    void  _move_key_tag_to_val_tag();
+    void  _move_key_tag2_to_key_tag();
+    void  _move_val_anchor_to_key_anchor();
+    void  _move_key_anchor_to_val_anchor();
+
+    void  _push_level(bool explicit_flow_chars = false);
+    void  _pop_level();
+
+    void  _start_unk(bool as_child=true);
+
+    void  _start_map(bool as_child=true);
+    void  _start_map_unk(bool as_child);
+    void  _stop_map();
+
+    void  _start_seq(bool as_child=true);
+    void  _stop_seq();
+
+    void  _start_seqimap();
+    void  _stop_seqimap();
+
+    void  _start_doc(bool as_child=true);
+    void  _stop_doc();
+    void  _start_new_doc(csubstr rem);
+    void  _end_stream();
+
+    NodeData* _append_val(csubstr val, flag_t quoted=false);
+    NodeData* _append_key_val(csubstr val, flag_t val_quoted=false);
+    bool  _rval_dash_start_or_continue_seq();
+
+    void  _store_scalar(csubstr s, flag_t is_quoted);
+    csubstr _consume_scalar();
+    void  _move_scalar_from_top();
+
+    inline NodeData* _append_val_null(const char *str) { _RYML_CB_ASSERT(m_stack.m_callbacks, str >= m_buf.begin() && str <= m_buf.end()); return _append_val({nullptr, size_t(0)}); }
+    inline NodeData* _append_key_val_null(const char *str) { _RYML_CB_ASSERT(m_stack.m_callbacks, str >= m_buf.begin() && str <= m_buf.end()); return _append_key_val({nullptr, size_t(0)}); }
+    inline void      _store_scalar_null(const char *str) {  _RYML_CB_ASSERT(m_stack.m_callbacks, str >= m_buf.begin() && str <= m_buf.end()); _store_scalar({nullptr, size_t(0)}, false); }
+
+    void  _set_indentation(size_t behind);
+    void  _save_indentation(size_t behind=0);
+    bool  _maybe_set_indentation_from_anchor_or_tag();
+
+    void  _write_key_anchor(size_t node_id);
+    void  _write_val_anchor(size_t node_id);
+
+    void _handle_directive(csubstr directive);
+
+    void _skipchars(char c);
+    template<size_t N>
+    void _skipchars(const char (&chars)[N]);
+
+private:
+
+    static size_t _count_nlines(csubstr src);
+
+private:
+
+    typedef enum : flag_t {
+        RTOP = 0x01 <<  0,   ///< reading at top level
+        RUNK = 0x01 <<  1,   ///< reading an unknown: must determine whether scalar, map or seq
+        RMAP = 0x01 <<  2,   ///< reading a map
+        RSEQ = 0x01 <<  3,   ///< reading a seq
+        FLOW = 0x01 <<  4,   ///< reading is inside explicit flow chars: [] or {}
+        QMRK = 0x01 <<  5,   ///< reading an explicit key (`? key`)
+        RKEY = 0x01 <<  6,   ///< reading a scalar as key
+        RVAL = 0x01 <<  7,   ///< reading a scalar as val
+        RNXT = 0x01 <<  8,   ///< read next val or keyval
+        SSCL = 0x01 <<  9,   ///< there's a stored scalar
+        QSCL = 0x01 << 10,   ///< stored scalar was quoted
+        RSET = 0x01 << 11,   ///< the (implicit) map being read is a !!set. @see https://yaml.org/type/set.html
+        NDOC = 0x01 << 12,   ///< no document mode. a document has ended and another has not started yet.
+        //! reading an implicit map nested in an explicit seq.
+        //! eg, {key: [key2: value2, key3: value3]}
+        //! is parsed as {key: [{key2: value2}, {key3: value3}]}
+        RSEQIMAP = 0x01 << 13,
+    } State_e;
+
+    struct LineContents
+    {
+        csubstr  full;        ///< the full line, including newlines on the right
+        csubstr  stripped;    ///< the stripped line, excluding newlines on the right
+        csubstr  rem;         ///< the stripped line remainder; initially starts at the first non-space character
+        size_t   indentation; ///< the number of spaces on the beginning of the line
+
+        LineContents() : full(), stripped(), rem(), indentation() {}
+
+        void reset_with_next_line(csubstr buf, size_t pos);
+
+        void reset(csubstr full_, csubstr stripped_)
+        {
+            full = full_;
+            stripped = stripped_;
+            rem = stripped_;
+            // find the first column where the character is not a space
+            indentation = full.first_not_of(' ');
+        }
+
+        size_t current_col() const
+        {
+            return current_col(rem);
+        }
+
+        size_t current_col(csubstr s) const
+        {
+            RYML_ASSERT(s.str >= full.str);
+            RYML_ASSERT(full.is_super(s));
+            size_t col = static_cast<size_t>(s.str - full.str);
+            return col;
+        }
+    };
+
+    struct State
+    {
+        flag_t       flags;
+        size_t       level;
+        size_t       node_id; // don't hold a pointer to the node as it will be relocated during tree resizes
+        csubstr      scalar;
+        size_t       scalar_col; // the column where the scalar (or its quotes) begin
+
+        Location     pos;
+        LineContents line_contents;
+        size_t       indref;
+
+        State() : flags(), level(), node_id(), scalar(), scalar_col(), pos(), line_contents(), indref() {}
+
+        void reset(const char *file, size_t node_id_)
+        {
+            flags = RUNK|RTOP;
+            level = 0;
+            pos.name = to_csubstr(file);
+            pos.offset = 0;
+            pos.line = 1;
+            pos.col = 1;
+            node_id = node_id_;
+            scalar_col = 0;
+            scalar.clear();
+            indref = 0;
+        }
+    };
+
+    void _line_progressed(size_t ahead);
+    void _line_ended();
+    void _line_ended_undo();
+
+    void _prepare_pop()
+    {
+        RYML_ASSERT(m_stack.size() > 1);
+        State const& curr = m_stack.top();
+        State      & next = m_stack.top(1);
+        next.pos = curr.pos;
+        next.line_contents = curr.line_contents;
+        next.scalar = curr.scalar;
+    }
+
+    inline bool _at_line_begin() const
+    {
+        return m_state->line_contents.rem.begin() == m_state->line_contents.full.begin();
+    }
+    inline bool _at_line_end() const
+    {
+        csubstr r = m_state->line_contents.rem;
+        return r.empty() || r.begins_with(' ', r.len);
+    }
+    inline bool _token_is_from_this_line(csubstr token) const
+    {
+        return token.is_sub(m_state->line_contents.full);
+    }
+
+    inline NodeData * node(State const* s) const { return m_tree->get(s->node_id); }
+    inline NodeData * node(State const& s) const { return m_tree->get(s .node_id); }
+    inline NodeData * node(size_t node_id) const { return m_tree->get(   node_id); }
+
+    inline bool has_all(flag_t f) const { return (m_state->flags & f) == f; }
+    inline bool has_any(flag_t f) const { return (m_state->flags & f) != 0; }
+    inline bool has_none(flag_t f) const { return (m_state->flags & f) == 0; }
+
+    static inline bool has_all(flag_t f, State const* s) { return (s->flags & f) == f; }
+    static inline bool has_any(flag_t f, State const* s) { return (s->flags & f) != 0; }
+    static inline bool has_none(flag_t f, State const* s) { return (s->flags & f) == 0; }
+
+    inline void set_flags(flag_t f) { set_flags(f, m_state); }
+    inline void add_flags(flag_t on) { add_flags(on, m_state); }
+    inline void addrem_flags(flag_t on, flag_t off) { addrem_flags(on, off, m_state); }
+    inline void rem_flags(flag_t off) { rem_flags(off, m_state); }
+
+    void set_flags(flag_t f, State * s);
+    void add_flags(flag_t on, State * s);
+    void addrem_flags(flag_t on, flag_t off, State * s);
+    void rem_flags(flag_t off, State * s);
+
+    void _resize_filter_arena(size_t num_characters);
+    void _grow_filter_arena(size_t num_characters);
+    substr _finish_filter_arena(substr dst, size_t pos);
+
+    void _prepare_locations();
+    void _resize_locations(size_t sz);
+    bool _locations_dirty() const;
+
+    bool _location_from_cont(Tree const& tree, size_t node, Location *C4_RESTRICT loc) const;
+    bool _location_from_node(Tree const& tree, size_t node, Location *C4_RESTRICT loc, size_t level) const;
+
+private:
+
+    void _free();
+    void _clr();
+    void _cp(Parser const* that);
+    void _mv(Parser *that);
+
+#ifdef RYML_DBG
+    template<class ...Args> void _dbg(csubstr fmt, Args const& C4_RESTRICT ...args) const;
+#endif
+    template<class ...Args> void _err(csubstr fmt, Args const& C4_RESTRICT ...args) const;
+    template<class DumpFn>  void _fmt_msg(DumpFn &&dumpfn) const;
+    static csubstr _prfl(substr buf, flag_t v);
+
+private:
+
+    ParserOptions m_options;
+
+    csubstr m_file;
+     substr m_buf;
+
+    size_t  m_root_id;
+    Tree *  m_tree;
+
+    detail::stack<State> m_stack;
+    State * m_state;
+
+    size_t  m_key_tag_indentation;
+    size_t  m_key_tag2_indentation;
+    csubstr m_key_tag;
+    csubstr m_key_tag2;
+    size_t  m_val_tag_indentation;
+    csubstr m_val_tag;
+
+    bool    m_key_anchor_was_before;
+    size_t  m_key_anchor_indentation;
+    csubstr m_key_anchor;
+    size_t  m_val_anchor_indentation;
+    csubstr m_val_anchor;
+
+    substr m_filter_arena;
+
+    size_t *m_newline_offsets;
+    size_t  m_newline_offsets_size;
+    size_t  m_newline_offsets_capacity;
+    csubstr m_newline_offsets_buf;
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** @name parse_in_place
+ *
+ * @desc parse a mutable YAML source buffer.
+ *
+ * @note These freestanding functions use a temporary parser object,
+ * and are convenience functions to easily parse YAML without the need
+ * to instantiate a separate parser. Note that some properties
+ * (notably node locations in the original source code) are only
+ * available through the parser object after it has parsed the
+ * code. If you need access to any of these properties, use
+ * Parser::parse_in_place() */
+/** @{ */
+
+inline Tree parse_in_place(                  substr yaml                         ) { Parser np; return np.parse_in_place({}      , yaml); } //!< parse in-situ a modifiable YAML source buffer.
+inline Tree parse_in_place(csubstr filename, substr yaml                         ) { Parser np; return np.parse_in_place(filename, yaml); } //!< parse in-situ a modifiable YAML source buffer, providing a filename for error messages.
+inline void parse_in_place(                  substr yaml, Tree *t                ) { Parser np; np.parse_in_place({}      , yaml, t); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer
+inline void parse_in_place(csubstr filename, substr yaml, Tree *t                ) { Parser np; np.parse_in_place(filename, yaml, t); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer, providing a filename for error messages.
+inline void parse_in_place(                  substr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_place({}      , yaml, t, node_id); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer
+inline void parse_in_place(csubstr filename, substr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_place(filename, yaml, t, node_id); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer, providing a filename for error messages.
+inline void parse_in_place(                  substr yaml, NodeRef node           ) { Parser np; np.parse_in_place({}      , yaml, node); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer
+inline void parse_in_place(csubstr filename, substr yaml, NodeRef node           ) { Parser np; np.parse_in_place(filename, yaml, node); } //!< reusing the YAML tree, parse in-situ a modifiable YAML source buffer, providing a filename for error messages.
+
+RYML_DEPRECATED("use parse_in_place() instead") inline Tree parse(                  substr yaml                         ) { Parser np; return np.parse_in_place({}      , yaml); }
+RYML_DEPRECATED("use parse_in_place() instead") inline Tree parse(csubstr filename, substr yaml                         ) { Parser np; return np.parse_in_place(filename, yaml); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(                  substr yaml, Tree *t                ) { Parser np; np.parse_in_place({}      , yaml, t); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(csubstr filename, substr yaml, Tree *t                ) { Parser np; np.parse_in_place(filename, yaml, t); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(                  substr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_place({}      , yaml, t, node_id); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(csubstr filename, substr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_place(filename, yaml, t, node_id); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(                  substr yaml, NodeRef node           ) { Parser np; np.parse_in_place({}      , yaml, node); }
+RYML_DEPRECATED("use parse_in_place() instead") inline void parse(csubstr filename, substr yaml, NodeRef node           ) { Parser np; np.parse_in_place(filename, yaml, node); }
+
+/** @} */
+
+
+//-----------------------------------------------------------------------------
+
+/** @name parse_in_arena
+ * @desc parse a read-only YAML source buffer, copying it first to the tree's arena.
+ *
+ * @note These freestanding functions use a temporary parser object,
+ * and are convenience functions to easily parse YAML without the need
+ * to instantiate a separate parser. Note that some properties
+ * (notably node locations in the original source code) are only
+ * available through the parser object after it has parsed the
+ * code. If you need access to any of these properties, use
+ * Parser::parse_in_arena().
+ *
+ * @note overloads receiving a substr YAML buffer are intentionally
+ * left undefined, such that calling parse_in_arena() with a substr
+ * will cause a linker error. This is to prevent an accidental
+ * copy of the source buffer to the tree's arena, because substr
+ * is implicitly convertible to csubstr. If you really intend to parse
+ * a mutable buffer in the tree's arena, convert it first to immutable
+ * by assigning the substr to a csubstr prior to calling parse_in_arena().
+ * This is not needed for parse_in_place() because csubstr is not
+ * implicitly convertible to substr. */
+/** @{ */
+
+/* READ THE NOTE ABOVE! */
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) Tree parse_in_arena(                  substr yaml                         );
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) Tree parse_in_arena(csubstr filename, substr yaml                         );
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(                  substr yaml, Tree *t                );
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr yaml, Tree *t                );
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(                  substr yaml, Tree *t, size_t node_id);
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr yaml, Tree *t, size_t node_id);
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(                  substr yaml, NodeRef node           );
+RYML_DEPRECATED(RYML_DONT_PARSE_SUBSTR_IN_ARENA) void parse_in_arena(csubstr filename, substr yaml, NodeRef node           );
+
+inline Tree parse_in_arena(                  csubstr yaml                         ) { Parser np; return np.parse_in_arena({}      , yaml); } //!< parse a read-only YAML source buffer, copying it first to the tree's source arena.
+inline Tree parse_in_arena(csubstr filename, csubstr yaml                         ) { Parser np; return np.parse_in_arena(filename, yaml); } //!< parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+inline void parse_in_arena(                  csubstr yaml, Tree *t                ) { Parser np; np.parse_in_arena({}      , yaml, t); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+inline void parse_in_arena(csubstr filename, csubstr yaml, Tree *t                ) { Parser np; np.parse_in_arena(filename, yaml, t); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+inline void parse_in_arena(                  csubstr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_arena({}      , yaml, t, node_id); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+inline void parse_in_arena(csubstr filename, csubstr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_arena(filename, yaml, t, node_id); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+inline void parse_in_arena(                  csubstr yaml, NodeRef node           ) { Parser np; np.parse_in_arena({}      , yaml, node); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+inline void parse_in_arena(csubstr filename, csubstr yaml, NodeRef node           ) { Parser np; np.parse_in_arena(filename, yaml, node); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+
+RYML_DEPRECATED("use parse_in_arena() instead") inline Tree parse(                  csubstr yaml                         ) { Parser np; return np.parse_in_arena({}      , yaml); } //!< parse a read-only YAML source buffer, copying it first to the tree's source arena.
+RYML_DEPRECATED("use parse_in_arena() instead") inline Tree parse(csubstr filename, csubstr yaml                         ) { Parser np; return np.parse_in_arena(filename, yaml); } //!< parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(                  csubstr yaml, Tree *t                ) { Parser np; np.parse_in_arena({}      , yaml, t); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(csubstr filename, csubstr yaml, Tree *t                ) { Parser np; np.parse_in_arena(filename, yaml, t); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(                  csubstr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_arena({}      , yaml, t, node_id); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(csubstr filename, csubstr yaml, Tree *t, size_t node_id) { Parser np; np.parse_in_arena(filename, yaml, t, node_id); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(                  csubstr yaml, NodeRef node           ) { Parser np; np.parse_in_arena({}      , yaml, node); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena.
+RYML_DEPRECATED("use parse_in_arena() instead") inline void parse(csubstr filename, csubstr yaml, NodeRef node           ) { Parser np; np.parse_in_arena(filename, yaml, node); } //!< reusing the YAML tree, parse a read-only YAML source buffer, copying it first to the tree's source arena, providing a filename for error messages.
+
+/** @} */
+
+} // namespace yml
+} // namespace c4
+
+#if defined(_MSC_VER)
+#   pragma warning(pop)
+#endif
+
+#endif /* _C4_YML_PARSE_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/preprocess.cpp b/thirdparty/ryml/src/c4/yml/preprocess.cpp
new file mode 100644
index 000000000..2e92dce14
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/preprocess.cpp
@@ -0,0 +1,110 @@
+#include "c4/yml/preprocess.hpp"
+#include "c4/yml/detail/parser_dbg.hpp"
+
+/** @file preprocess.hpp Functions for preprocessing YAML prior to parsing. */
+
+namespace c4 {
+namespace yml {
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+namespace {
+C4_ALWAYS_INLINE bool _is_idchar(char c)
+{
+    return (c >= 'a' && c <= 'z')
+        || (c >= 'A' && c <= 'Z')
+        || (c >= '0' && c <= '9')
+        || (c == '_' || c == '-' || c == '~' || c == '$');
+}
+
+typedef enum { kReadPending = 0, kKeyPending = 1, kValPending = 2 } _ppstate;
+C4_ALWAYS_INLINE _ppstate _next(_ppstate s)
+{
+    int n = (int)s + 1;
+    return (_ppstate)(n <= (int)kValPending ? n : 0);
+}
+} // empty namespace
+
+
+//-----------------------------------------------------------------------------
+
+size_t preprocess_rxmap(csubstr s, substr buf)
+{
+    detail::_SubstrWriter writer(buf);
+    _ppstate state = kReadPending;
+    size_t last = 0;
+
+    if(s.begins_with('{'))
+    {
+        RYML_CHECK(s.ends_with('}'));
+        s = s.offs(1, 1);
+    }
+
+    writer.append('{');
+
+    for(size_t i = 0; i < s.len; ++i)
+    {
+        const char curr = s[i];
+        const char next = i+1 < s.len ? s[i+1] : '\0';
+
+        if(curr == '\'' || curr == '"')
+        {
+            csubstr ss = s.sub(i).pair_range_esc(curr, '\\');
+            i += static_cast<size_t>(ss.end() - (s.str + i));
+            state = _next(state);
+        }
+        else if(state == kReadPending && _is_idchar(curr))
+        {
+            state = _next(state);
+        }
+
+        switch(state)
+        {
+        case kKeyPending:
+        {
+            if(curr == ':' && next == ' ')
+            {
+                state = _next(state);
+            }
+            else if(curr == ',' && next == ' ')
+            {
+                writer.append(s.range(last, i));
+                writer.append(": 1, ");
+                last = i + 2;
+            }
+            break;
+        }
+        case kValPending:
+        {
+            if(curr == '[' || curr == '{' || curr == '(')
+            {
+                csubstr ss = s.sub(i).pair_range_nested(curr, '\\');
+                i += static_cast<size_t>(ss.end() - (s.str + i));
+                state = _next(state);
+            }
+            else if(curr == ',' && next == ' ')
+            {
+                state = _next(state);
+            }
+            break;
+        }
+        default:
+            // nothing to do
+            break;
+        }
+    }
+
+    writer.append(s.sub(last));
+    if(state == kKeyPending)
+        writer.append(": 1");
+    writer.append('}');
+
+    return writer.pos;
+}
+
+
+} // namespace yml
+} // namespace c4
diff --git a/thirdparty/ryml/src/c4/yml/preprocess.hpp b/thirdparty/ryml/src/c4/yml/preprocess.hpp
new file mode 100644
index 000000000..def066389
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/preprocess.hpp
@@ -0,0 +1,99 @@
+#ifndef _C4_YML_PREPROCESS_HPP_
+#define _C4_YML_PREPROCESS_HPP_
+
+/** @file preprocess.hpp Functions for preprocessing YAML prior to parsing. */
+
+/** @defgroup Preprocessors Preprocessor functions
+ *
+ * These are the existing preprocessors:
+ *
+ * @code{.cpp}
+ * size_t preprocess_json(csubstr json, substr buf)
+ * size_t preprocess_rxmap(csubstr json, substr buf)
+ * @endcode
+ */
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "./common.hpp"
+#endif
+#include <c4/substr.hpp>
+
+
+namespace c4 {
+namespace yml {
+
+namespace detail {
+using Preprocessor = size_t(csubstr, substr);
+template<Preprocessor PP, class CharContainer>
+substr preprocess_into_container(csubstr input, CharContainer *out)
+{
+    // try to write once. the preprocessor will stop writing at the end of
+    // the container, but will process all the input to determine the
+    // required container size.
+    size_t sz = PP(input, to_substr(*out));
+    // if the container size is not enough, resize, and run again in the
+    // resized container
+    if(sz > out->size())
+    {
+        out->resize(sz);
+        sz = PP(input, to_substr(*out));
+    }
+    return to_substr(*out).first(sz);
+}
+} // namespace detail
+
+
+//-----------------------------------------------------------------------------
+
+/** @name preprocess_rxmap
+ * Convert flow-type relaxed maps (with implicit bools) into strict YAML
+ * flow map.
+ *
+ * @code{.yaml}
+ * {a, b, c, d: [e, f], g: {a, b}}
+ * # is converted into this:
+ * {a: 1, b: 1, c: 1, d: [e, f], g: {a, b}}
+ * @endcode
+
+ * @note this is NOT recursive - conversion happens only in the top-level map
+ * @param rxmap A relaxed map
+ * @param buf output buffer
+ * @param out output container
+ */
+
+//@{
+
+/** Write into a given output buffer. This function is safe to call with
+ * empty or small buffers; it won't write beyond the end of the buffer.
+ *
+ * @return the number of characters required for output
+ */
+RYML_EXPORT size_t preprocess_rxmap(csubstr rxmap, substr buf);
+
+
+/** Write into an existing container. It is resized to contained the output.
+ * @return a substr of the container
+ * @overload preprocess_rxmap */
+template<class CharContainer>
+substr preprocess_rxmap(csubstr rxmap, CharContainer *out)
+{
+    return detail::preprocess_into_container<preprocess_rxmap>(rxmap, out);
+}
+
+
+/** Create a container with the result.
+ * @overload preprocess_rxmap */
+template<class CharContainer>
+CharContainer preprocess_rxmap(csubstr rxmap)
+{
+    CharContainer out;
+    preprocess_rxmap(rxmap, &out);
+    return out;
+}
+
+//@}
+
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_PREPROCESS_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/std/map.hpp b/thirdparty/ryml/src/c4/yml/std/map.hpp
new file mode 100644
index 000000000..fc48dc5e6
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/std/map.hpp
@@ -0,0 +1,45 @@
+#ifndef _C4_YML_STD_MAP_HPP_
+#define _C4_YML_STD_MAP_HPP_
+
+/** @file map.hpp write/read std::map to/from a YAML tree. */
+
+#include "c4/yml/node.hpp"
+#include <map>
+
+namespace c4 {
+namespace yml {
+
+// std::map requires child nodes in the data
+// tree hierarchy (a MAP node in ryml parlance).
+// So it should be serialized via write()/read().
+
+template<class K, class V, class Less, class Alloc>
+void write(c4::yml::NodeRef *n, std::map<K, V, Less, Alloc> const& m)
+{
+    *n |= c4::yml::MAP;
+    for(auto const& C4_RESTRICT p : m)
+    {
+        auto ch = n->append_child();
+        ch << c4::yml::key(p.first);
+        ch << p.second;
+    }
+}
+
+template<class K, class V, class Less, class Alloc>
+bool read(c4::yml::ConstNodeRef const& n, std::map<K, V, Less, Alloc> * m)
+{
+    K k{};
+    V v{};
+    for(auto const& C4_RESTRICT ch : n)
+    {
+        ch >> c4::yml::key(k);
+        ch >> v;
+        m->emplace(std::make_pair(std::move(k), std::move(v)));
+    }
+    return true;
+}
+
+} // namespace yml
+} // namespace c4
+
+#endif // _C4_YML_STD_MAP_HPP_
diff --git a/thirdparty/ryml/src/c4/yml/std/std.hpp b/thirdparty/ryml/src/c4/yml/std/std.hpp
new file mode 100644
index 000000000..08e80d155
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/std/std.hpp
@@ -0,0 +1,8 @@
+#ifndef _C4_YML_STD_STD_HPP_
+#define _C4_YML_STD_STD_HPP_
+
+#include "c4/yml/std/string.hpp"
+#include "c4/yml/std/vector.hpp"
+#include "c4/yml/std/map.hpp"
+
+#endif // _C4_YML_STD_STD_HPP_
diff --git a/thirdparty/ryml/src/c4/yml/std/string.hpp b/thirdparty/ryml/src/c4/yml/std/string.hpp
new file mode 100644
index 000000000..e3318f91c
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/std/string.hpp
@@ -0,0 +1,9 @@
+#ifndef C4_YML_STD_STRING_HPP_
+#define C4_YML_STD_STRING_HPP_
+
+/** @file string.hpp substring conversions for/from std::string */
+
+// everything we need is implemented here:
+#include <c4/std/string.hpp>
+
+#endif // C4_YML_STD_STRING_HPP_
diff --git a/thirdparty/ryml/src/c4/yml/std/vector.hpp b/thirdparty/ryml/src/c4/yml/std/vector.hpp
new file mode 100644
index 000000000..1b6a4610a
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/std/vector.hpp
@@ -0,0 +1,53 @@
+#ifndef _C4_YML_STD_VECTOR_HPP_
+#define _C4_YML_STD_VECTOR_HPP_
+
+#include "c4/yml/node.hpp"
+#include <c4/std/vector.hpp>
+#include <vector>
+
+namespace c4 {
+namespace yml {
+
+// vector is a sequence-like type, and it requires child nodes
+// in the data tree hierarchy (a SEQ node in ryml parlance).
+// So it should be serialized via write()/read().
+
+
+template<class V, class Alloc>
+void write(c4::yml::NodeRef *n, std::vector<V, Alloc> const& vec)
+{
+    *n |= c4::yml::SEQ;
+    for(auto const& v : vec)
+        n->append_child() << v;
+}
+
+template<class V, class Alloc>
+bool read(c4::yml::ConstNodeRef const& n, std::vector<V, Alloc> *vec)
+{
+    vec->resize(n.num_children());
+    size_t pos = 0;
+    for(auto const ch : n)
+        ch >> (*vec)[pos++];
+    return true;
+}
+
+/** specialization: std::vector<bool> uses std::vector<bool>::reference as
+ * the return value of its operator[]. */
+template<class Alloc>
+bool read(c4::yml::ConstNodeRef const& n, std::vector<bool, Alloc> *vec)
+{
+    vec->resize(n.num_children());
+    size_t pos = 0;
+    bool tmp;
+    for(auto const ch : n)
+    {
+        ch >> tmp;
+        (*vec)[pos++] = tmp;
+    }
+    return true;
+}
+
+} // namespace yml
+} // namespace c4
+
+#endif // _C4_YML_STD_VECTOR_HPP_
diff --git a/thirdparty/ryml/src/c4/yml/tree.cpp b/thirdparty/ryml/src/c4/yml/tree.cpp
new file mode 100644
index 000000000..b16ff8f5d
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/tree.cpp
@@ -0,0 +1,2183 @@
+#include "c4/yml/tree.hpp"
+#include "c4/yml/detail/parser_dbg.hpp"
+#include "c4/yml/node.hpp"
+#include "c4/yml/detail/stack.hpp"
+
+
+C4_SUPPRESS_WARNING_GCC_WITH_PUSH("-Wtype-limits")
+C4_SUPPRESS_WARNING_MSVC_WITH_PUSH(4296/*expression is always 'boolean_value'*/)
+
+namespace c4 {
+namespace yml {
+
+
+csubstr normalize_tag(csubstr tag)
+{
+    YamlTag_e t = to_tag(tag);
+    if(t != TAG_NONE)
+        return from_tag(t);
+    if(tag.begins_with("!<"))
+        tag = tag.sub(1);
+    if(tag.begins_with("<!"))
+        return tag;
+    return tag;
+}
+
+csubstr normalize_tag_long(csubstr tag)
+{
+    YamlTag_e t = to_tag(tag);
+    if(t != TAG_NONE)
+        return from_tag_long(t);
+    if(tag.begins_with("!<"))
+        tag = tag.sub(1);
+    if(tag.begins_with("<!"))
+        return tag;
+    return tag;
+}
+
+YamlTag_e to_tag(csubstr tag)
+{
+    if(tag.begins_with("!<"))
+        tag = tag.sub(1);
+    if(tag.begins_with("!!"))
+        tag = tag.sub(2);
+    else if(tag.begins_with('!'))
+        return TAG_NONE;
+    else if(tag.begins_with("tag:yaml.org,2002:"))
+    {
+        RYML_ASSERT(csubstr("tag:yaml.org,2002:").len == 18);
+        tag = tag.sub(18);
+    }
+    else if(tag.begins_with("<tag:yaml.org,2002:"))
+    {
+        RYML_ASSERT(csubstr("<tag:yaml.org,2002:").len == 19);
+        tag = tag.sub(19);
+        if(!tag.len)
+            return TAG_NONE;
+        tag = tag.offs(0, 1);
+    }
+
+    if(tag == "map")
+        return TAG_MAP;
+    else if(tag == "omap")
+        return TAG_OMAP;
+    else if(tag == "pairs")
+        return TAG_PAIRS;
+    else if(tag == "set")
+        return TAG_SET;
+    else if(tag == "seq")
+        return TAG_SEQ;
+    else if(tag == "binary")
+        return TAG_BINARY;
+    else if(tag == "bool")
+        return TAG_BOOL;
+    else if(tag == "float")
+        return TAG_FLOAT;
+    else if(tag == "int")
+        return TAG_INT;
+    else if(tag == "merge")
+        return TAG_MERGE;
+    else if(tag == "null")
+        return TAG_NULL;
+    else if(tag == "str")
+        return TAG_STR;
+    else if(tag == "timestamp")
+        return TAG_TIMESTAMP;
+    else if(tag == "value")
+        return TAG_VALUE;
+
+    return TAG_NONE;
+}
+
+csubstr from_tag_long(YamlTag_e tag)
+{
+    switch(tag)
+    {
+    case TAG_MAP:
+        return {"<tag:yaml.org,2002:map>"};
+    case TAG_OMAP:
+        return {"<tag:yaml.org,2002:omap>"};
+    case TAG_PAIRS:
+        return {"<tag:yaml.org,2002:pairs>"};
+    case TAG_SET:
+        return {"<tag:yaml.org,2002:set>"};
+    case TAG_SEQ:
+        return {"<tag:yaml.org,2002:seq>"};
+    case TAG_BINARY:
+        return {"<tag:yaml.org,2002:binary>"};
+    case TAG_BOOL:
+        return {"<tag:yaml.org,2002:bool>"};
+    case TAG_FLOAT:
+        return {"<tag:yaml.org,2002:float>"};
+    case TAG_INT:
+        return {"<tag:yaml.org,2002:int>"};
+    case TAG_MERGE:
+        return {"<tag:yaml.org,2002:merge>"};
+    case TAG_NULL:
+        return {"<tag:yaml.org,2002:null>"};
+    case TAG_STR:
+        return {"<tag:yaml.org,2002:str>"};
+    case TAG_TIMESTAMP:
+        return {"<tag:yaml.org,2002:timestamp>"};
+    case TAG_VALUE:
+        return {"<tag:yaml.org,2002:value>"};
+    case TAG_YAML:
+        return {"<tag:yaml.org,2002:yaml>"};
+    case TAG_NONE:
+        return {""};
+    }
+    return {""};
+}
+
+csubstr from_tag(YamlTag_e tag)
+{
+    switch(tag)
+    {
+    case TAG_MAP:
+        return {"!!map"};
+    case TAG_OMAP:
+        return {"!!omap"};
+    case TAG_PAIRS:
+        return {"!!pairs"};
+    case TAG_SET:
+        return {"!!set"};
+    case TAG_SEQ:
+        return {"!!seq"};
+    case TAG_BINARY:
+        return {"!!binary"};
+    case TAG_BOOL:
+        return {"!!bool"};
+    case TAG_FLOAT:
+        return {"!!float"};
+    case TAG_INT:
+        return {"!!int"};
+    case TAG_MERGE:
+        return {"!!merge"};
+    case TAG_NULL:
+        return {"!!null"};
+    case TAG_STR:
+        return {"!!str"};
+    case TAG_TIMESTAMP:
+        return {"!!timestamp"};
+    case TAG_VALUE:
+        return {"!!value"};
+    case TAG_YAML:
+        return {"!!yaml"};
+    case TAG_NONE:
+        return {""};
+    }
+    return {""};
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+const char* NodeType::type_str(NodeType_e ty)
+{
+    switch(ty & _TYMASK)
+    {
+    case KEYVAL:
+        return "KEYVAL";
+    case KEY:
+        return "KEY";
+    case VAL:
+        return "VAL";
+    case MAP:
+        return "MAP";
+    case SEQ:
+        return "SEQ";
+    case KEYMAP:
+        return "KEYMAP";
+    case KEYSEQ:
+        return "KEYSEQ";
+    case DOCSEQ:
+        return "DOCSEQ";
+    case DOCMAP:
+        return "DOCMAP";
+    case DOCVAL:
+        return "DOCVAL";
+    case DOC:
+        return "DOC";
+    case STREAM:
+        return "STREAM";
+    case NOTYPE:
+        return "NOTYPE";
+    default:
+        if((ty & KEYVAL) == KEYVAL)
+            return "KEYVAL***";
+        if((ty & KEYMAP) == KEYMAP)
+            return "KEYMAP***";
+        if((ty & KEYSEQ) == KEYSEQ)
+            return "KEYSEQ***";
+        if((ty & DOCSEQ) == DOCSEQ)
+            return "DOCSEQ***";
+        if((ty & DOCMAP) == DOCMAP)
+            return "DOCMAP***";
+        if((ty & DOCVAL) == DOCVAL)
+            return "DOCVAL***";
+        if(ty & KEY)
+            return "KEY***";
+        if(ty & VAL)
+            return "VAL***";
+        if(ty & MAP)
+            return "MAP***";
+        if(ty & SEQ)
+            return "SEQ***";
+        if(ty & DOC)
+            return "DOC***";
+        return "(unk)";
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+NodeRef Tree::rootref()
+{
+    return NodeRef(this, root_id());
+}
+ConstNodeRef Tree::rootref() const
+{
+    return ConstNodeRef(this, root_id());
+}
+
+ConstNodeRef Tree::crootref()
+{
+    return ConstNodeRef(this, root_id());
+}
+ConstNodeRef Tree::crootref() const
+{
+    return ConstNodeRef(this, root_id());
+}
+
+NodeRef Tree::ref(size_t id)
+{
+    _RYML_CB_ASSERT(m_callbacks, id != NONE && id >= 0 && id < m_size);
+    return NodeRef(this, id);
+}
+ConstNodeRef Tree::ref(size_t id) const
+{
+    _RYML_CB_ASSERT(m_callbacks, id != NONE && id >= 0 && id < m_size);
+    return ConstNodeRef(this, id);
+}
+
+ConstNodeRef Tree::cref(size_t id)
+{
+    _RYML_CB_ASSERT(m_callbacks, id != NONE && id >= 0 && id < m_size);
+    return ConstNodeRef(this, id);
+}
+ConstNodeRef Tree::cref(size_t id) const
+{
+    _RYML_CB_ASSERT(m_callbacks, id != NONE && id >= 0 && id < m_size);
+    return ConstNodeRef(this, id);
+}
+
+NodeRef Tree::operator[] (csubstr key)
+{
+    return rootref()[key];
+}
+ConstNodeRef Tree::operator[] (csubstr key) const
+{
+    return rootref()[key];
+}
+
+NodeRef Tree::operator[] (size_t i)
+{
+    return rootref()[i];
+}
+ConstNodeRef Tree::operator[] (size_t i) const
+{
+    return rootref()[i];
+}
+
+NodeRef Tree::docref(size_t i)
+{
+    return ref(doc(i));
+}
+ConstNodeRef Tree::docref(size_t i) const
+{
+    return cref(doc(i));
+}
+
+
+//-----------------------------------------------------------------------------
+Tree::Tree(Callbacks const& cb)
+    : m_buf(nullptr)
+    , m_cap(0)
+    , m_size(0)
+    , m_free_head(NONE)
+    , m_free_tail(NONE)
+    , m_arena()
+    , m_arena_pos(0)
+    , m_callbacks(cb)
+{
+}
+
+Tree::Tree(size_t node_capacity, size_t arena_capacity, Callbacks const& cb)
+    : Tree(cb)
+{
+    reserve(node_capacity);
+    reserve_arena(arena_capacity);
+}
+
+Tree::~Tree()
+{
+    _free();
+}
+
+
+Tree::Tree(Tree const& that) noexcept : Tree(that.m_callbacks)
+{
+    _copy(that);
+}
+
+Tree& Tree::operator= (Tree const& that) noexcept
+{
+    _free();
+    m_callbacks = that.m_callbacks;
+    _copy(that);
+    return *this;
+}
+
+Tree::Tree(Tree && that) noexcept : Tree(that.m_callbacks)
+{
+    _move(that);
+}
+
+Tree& Tree::operator= (Tree && that) noexcept
+{
+    _free();
+    m_callbacks = that.m_callbacks;
+    _move(that);
+    return *this;
+}
+
+void Tree::_free()
+{
+    if(m_buf)
+    {
+        _RYML_CB_ASSERT(m_callbacks, m_cap > 0);
+        _RYML_CB_FREE(m_callbacks, m_buf, NodeData, m_cap);
+    }
+    if(m_arena.str)
+    {
+        _RYML_CB_ASSERT(m_callbacks, m_arena.len > 0);
+        _RYML_CB_FREE(m_callbacks, m_arena.str, char, m_arena.len);
+    }
+    _clear();
+}
+
+
+C4_SUPPRESS_WARNING_GCC_PUSH
+#if defined(__GNUC__) && __GNUC__>= 8
+    C4_SUPPRESS_WARNING_GCC_WITH_PUSH("-Wclass-memaccess") // error: ‘void* memset(void*, int, size_t)’ clearing an object of type ‘class c4::yml::Tree’ with no trivial copy-assignment; use assignment or value-initialization instead
+#endif
+
+void Tree::_clear()
+{
+    m_buf = nullptr;
+    m_cap = 0;
+    m_size = 0;
+    m_free_head = 0;
+    m_free_tail = 0;
+    m_arena = {};
+    m_arena_pos = 0;
+    for(size_t i = 0; i < RYML_MAX_TAG_DIRECTIVES; ++i)
+        m_tag_directives[i] = {};
+}
+
+void Tree::_copy(Tree const& that)
+{
+    _RYML_CB_ASSERT(m_callbacks, m_buf == nullptr);
+    _RYML_CB_ASSERT(m_callbacks, m_arena.str == nullptr);
+    _RYML_CB_ASSERT(m_callbacks, m_arena.len == 0);
+    m_buf = _RYML_CB_ALLOC_HINT(m_callbacks, NodeData, that.m_cap, that.m_buf);
+    memcpy(m_buf, that.m_buf, that.m_cap * sizeof(NodeData));
+    m_cap = that.m_cap;
+    m_size = that.m_size;
+    m_free_head = that.m_free_head;
+    m_free_tail = that.m_free_tail;
+    m_arena_pos = that.m_arena_pos;
+    m_arena = that.m_arena;
+    if(that.m_arena.str)
+    {
+        _RYML_CB_ASSERT(m_callbacks, that.m_arena.len > 0);
+        substr arena;
+        arena.str = _RYML_CB_ALLOC_HINT(m_callbacks, char, that.m_arena.len, that.m_arena.str);
+        arena.len = that.m_arena.len;
+        _relocate(arena); // does a memcpy of the arena and updates nodes using the old arena
+        m_arena = arena;
+    }
+    for(size_t i = 0; i < RYML_MAX_TAG_DIRECTIVES; ++i)
+        m_tag_directives[i] = that.m_tag_directives[i];
+}
+
+void Tree::_move(Tree & that)
+{
+    _RYML_CB_ASSERT(m_callbacks, m_buf == nullptr);
+    _RYML_CB_ASSERT(m_callbacks, m_arena.str == nullptr);
+    _RYML_CB_ASSERT(m_callbacks, m_arena.len == 0);
+    m_buf = that.m_buf;
+    m_cap = that.m_cap;
+    m_size = that.m_size;
+    m_free_head = that.m_free_head;
+    m_free_tail = that.m_free_tail;
+    m_arena = that.m_arena;
+    m_arena_pos = that.m_arena_pos;
+    for(size_t i = 0; i < RYML_MAX_TAG_DIRECTIVES; ++i)
+        m_tag_directives[i] = that.m_tag_directives[i];
+    that._clear();
+}
+
+void Tree::_relocate(substr next_arena)
+{
+    _RYML_CB_ASSERT(m_callbacks, next_arena.not_empty());
+    _RYML_CB_ASSERT(m_callbacks, next_arena.len >= m_arena.len);
+    memcpy(next_arena.str, m_arena.str, m_arena_pos);
+    for(NodeData *C4_RESTRICT n = m_buf, *e = m_buf + m_cap; n != e; ++n)
+    {
+        if(in_arena(n->m_key.scalar))
+            n->m_key.scalar = _relocated(n->m_key.scalar, next_arena);
+        if(in_arena(n->m_key.tag))
+            n->m_key.tag = _relocated(n->m_key.tag, next_arena);
+        if(in_arena(n->m_key.anchor))
+            n->m_key.anchor = _relocated(n->m_key.anchor, next_arena);
+        if(in_arena(n->m_val.scalar))
+            n->m_val.scalar = _relocated(n->m_val.scalar, next_arena);
+        if(in_arena(n->m_val.tag))
+            n->m_val.tag = _relocated(n->m_val.tag, next_arena);
+        if(in_arena(n->m_val.anchor))
+            n->m_val.anchor = _relocated(n->m_val.anchor, next_arena);
+    }
+    for(TagDirective &C4_RESTRICT td : m_tag_directives)
+    {
+        if(in_arena(td.prefix))
+            td.prefix = _relocated(td.prefix, next_arena);
+        if(in_arena(td.handle))
+            td.handle = _relocated(td.handle, next_arena);
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+void Tree::reserve(size_t cap)
+{
+    if(cap > m_cap)
+    {
+        NodeData *buf = _RYML_CB_ALLOC_HINT(m_callbacks, NodeData, cap, m_buf);
+        if(m_buf)
+        {
+            memcpy(buf, m_buf, m_cap * sizeof(NodeData));
+            _RYML_CB_FREE(m_callbacks, m_buf, NodeData, m_cap);
+        }
+        size_t first = m_cap, del = cap - m_cap;
+        m_cap = cap;
+        m_buf = buf;
+        _clear_range(first, del);
+        if(m_free_head != NONE)
+        {
+            _RYML_CB_ASSERT(m_callbacks, m_buf != nullptr);
+            _RYML_CB_ASSERT(m_callbacks, m_free_tail != NONE);
+            m_buf[m_free_tail].m_next_sibling = first;
+            m_buf[first].m_prev_sibling = m_free_tail;
+            m_free_tail = cap-1;
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_callbacks, m_free_tail == NONE);
+            m_free_head = first;
+            m_free_tail = cap-1;
+        }
+        _RYML_CB_ASSERT(m_callbacks, m_free_head == NONE || (m_free_head >= 0 && m_free_head < cap));
+        _RYML_CB_ASSERT(m_callbacks, m_free_tail == NONE || (m_free_tail >= 0 && m_free_tail < cap));
+
+        if( ! m_size)
+            _claim_root();
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+void Tree::clear()
+{
+    _clear_range(0, m_cap);
+    m_size = 0;
+    if(m_buf)
+    {
+        _RYML_CB_ASSERT(m_callbacks, m_cap >= 0);
+        m_free_head = 0;
+        m_free_tail = m_cap-1;
+        _claim_root();
+    }
+    else
+    {
+        m_free_head = NONE;
+        m_free_tail = NONE;
+    }
+    for(size_t i = 0; i < RYML_MAX_TAG_DIRECTIVES; ++i)
+        m_tag_directives[i] = {};
+}
+
+void Tree::_claim_root()
+{
+    size_t r = _claim();
+    _RYML_CB_ASSERT(m_callbacks, r == 0);
+    _set_hierarchy(r, NONE, NONE);
+}
+
+
+//-----------------------------------------------------------------------------
+void Tree::_clear_range(size_t first, size_t num)
+{
+    if(num == 0)
+        return; // prevent overflow when subtracting
+    _RYML_CB_ASSERT(m_callbacks, first >= 0 && first + num <= m_cap);
+    memset(m_buf + first, 0, num * sizeof(NodeData)); // TODO we should not need this
+    for(size_t i = first, e = first + num; i < e; ++i)
+    {
+        _clear(i);
+        NodeData *n = m_buf + i;
+        n->m_prev_sibling = i - 1;
+        n->m_next_sibling = i + 1;
+    }
+    m_buf[first + num - 1].m_next_sibling = NONE;
+}
+
+C4_SUPPRESS_WARNING_GCC_POP
+
+
+//-----------------------------------------------------------------------------
+void Tree::_release(size_t i)
+{
+    _RYML_CB_ASSERT(m_callbacks, i >= 0 && i < m_cap);
+
+    _rem_hierarchy(i);
+    _free_list_add(i);
+    _clear(i);
+
+    --m_size;
+}
+
+//-----------------------------------------------------------------------------
+// add to the front of the free list
+void Tree::_free_list_add(size_t i)
+{
+    _RYML_CB_ASSERT(m_callbacks, i >= 0 && i < m_cap);
+    NodeData &C4_RESTRICT w = m_buf[i];
+
+    w.m_parent = NONE;
+    w.m_next_sibling = m_free_head;
+    w.m_prev_sibling = NONE;
+    if(m_free_head != NONE)
+        m_buf[m_free_head].m_prev_sibling = i;
+    m_free_head = i;
+    if(m_free_tail == NONE)
+        m_free_tail = m_free_head;
+}
+
+void Tree::_free_list_rem(size_t i)
+{
+    if(m_free_head == i)
+        m_free_head = _p(i)->m_next_sibling;
+    _rem_hierarchy(i);
+}
+
+//-----------------------------------------------------------------------------
+size_t Tree::_claim()
+{
+    if(m_free_head == NONE || m_buf == nullptr)
+    {
+        size_t sz = 2 * m_cap;
+        sz = sz ? sz : 16;
+        reserve(sz);
+        _RYML_CB_ASSERT(m_callbacks, m_free_head != NONE);
+    }
+
+    _RYML_CB_ASSERT(m_callbacks, m_size < m_cap);
+    _RYML_CB_ASSERT(m_callbacks, m_free_head >= 0 && m_free_head < m_cap);
+
+    size_t ichild = m_free_head;
+    NodeData *child = m_buf + ichild;
+
+    ++m_size;
+    m_free_head = child->m_next_sibling;
+    if(m_free_head == NONE)
+    {
+        m_free_tail = NONE;
+        _RYML_CB_ASSERT(m_callbacks, m_size == m_cap);
+    }
+
+    _clear(ichild);
+
+    return ichild;
+}
+
+//-----------------------------------------------------------------------------
+
+C4_SUPPRESS_WARNING_GCC_PUSH
+C4_SUPPRESS_WARNING_CLANG_PUSH
+C4_SUPPRESS_WARNING_CLANG("-Wnull-dereference")
+#if defined(__GNUC__) && (__GNUC__ >= 6)
+C4_SUPPRESS_WARNING_GCC("-Wnull-dereference")
+#endif
+
+void Tree::_set_hierarchy(size_t ichild, size_t iparent, size_t iprev_sibling)
+{
+    _RYML_CB_ASSERT(m_callbacks, iparent == NONE || (iparent >= 0 && iparent < m_cap));
+    _RYML_CB_ASSERT(m_callbacks, iprev_sibling == NONE || (iprev_sibling >= 0 && iprev_sibling < m_cap));
+
+    NodeData *C4_RESTRICT child = get(ichild);
+
+    child->m_parent = iparent;
+    child->m_prev_sibling = NONE;
+    child->m_next_sibling = NONE;
+
+    if(iparent == NONE)
+    {
+        _RYML_CB_ASSERT(m_callbacks, ichild == 0);
+        _RYML_CB_ASSERT(m_callbacks, iprev_sibling == NONE);
+    }
+
+    if(iparent == NONE)
+        return;
+
+    size_t inext_sibling = iprev_sibling != NONE ? next_sibling(iprev_sibling) : first_child(iparent);
+    NodeData *C4_RESTRICT parent = get(iparent);
+    NodeData *C4_RESTRICT psib   = get(iprev_sibling);
+    NodeData *C4_RESTRICT nsib   = get(inext_sibling);
+
+    if(psib)
+    {
+        _RYML_CB_ASSERT(m_callbacks, next_sibling(iprev_sibling) == id(nsib));
+        child->m_prev_sibling = id(psib);
+        psib->m_next_sibling = id(child);
+        _RYML_CB_ASSERT(m_callbacks, psib->m_prev_sibling != psib->m_next_sibling || psib->m_prev_sibling == NONE);
+    }
+
+    if(nsib)
+    {
+        _RYML_CB_ASSERT(m_callbacks, prev_sibling(inext_sibling) == id(psib));
+        child->m_next_sibling = id(nsib);
+        nsib->m_prev_sibling = id(child);
+        _RYML_CB_ASSERT(m_callbacks, nsib->m_prev_sibling != nsib->m_next_sibling || nsib->m_prev_sibling == NONE);
+    }
+
+    if(parent->m_first_child == NONE)
+    {
+        _RYML_CB_ASSERT(m_callbacks, parent->m_last_child == NONE);
+        parent->m_first_child = id(child);
+        parent->m_last_child = id(child);
+    }
+    else
+    {
+        if(child->m_next_sibling == parent->m_first_child)
+            parent->m_first_child = id(child);
+
+        if(child->m_prev_sibling == parent->m_last_child)
+            parent->m_last_child = id(child);
+    }
+}
+
+C4_SUPPRESS_WARNING_GCC_POP
+C4_SUPPRESS_WARNING_CLANG_POP
+
+
+//-----------------------------------------------------------------------------
+void Tree::_rem_hierarchy(size_t i)
+{
+    _RYML_CB_ASSERT(m_callbacks, i >= 0 && i < m_cap);
+
+    NodeData &C4_RESTRICT w = m_buf[i];
+
+    // remove from the parent
+    if(w.m_parent != NONE)
+    {
+        NodeData &C4_RESTRICT p = m_buf[w.m_parent];
+        if(p.m_first_child == i)
+        {
+            p.m_first_child = w.m_next_sibling;
+        }
+        if(p.m_last_child == i)
+        {
+            p.m_last_child = w.m_prev_sibling;
+        }
+    }
+
+    // remove from the used list
+    if(w.m_prev_sibling != NONE)
+    {
+        NodeData *C4_RESTRICT prev = get(w.m_prev_sibling);
+        prev->m_next_sibling = w.m_next_sibling;
+    }
+    if(w.m_next_sibling != NONE)
+    {
+        NodeData *C4_RESTRICT next = get(w.m_next_sibling);
+        next->m_prev_sibling = w.m_prev_sibling;
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Tree::reorder()
+{
+    size_t r = root_id();
+    _do_reorder(&r, 0);
+}
+
+//-----------------------------------------------------------------------------
+size_t Tree::_do_reorder(size_t *node, size_t count)
+{
+    // swap this node if it's not in place
+    if(*node != count)
+    {
+        _swap(*node, count);
+        *node = count;
+    }
+    ++count; // bump the count from this node
+
+    // now descend in the hierarchy
+    for(size_t i = first_child(*node); i != NONE; i = next_sibling(i))
+    {
+        // this child may have been relocated to a different index,
+        // so get an updated version
+        count = _do_reorder(&i, count);
+    }
+    return count;
+}
+
+//-----------------------------------------------------------------------------
+void Tree::_swap(size_t n_, size_t m_)
+{
+    _RYML_CB_ASSERT(m_callbacks, (parent(n_) != NONE) || type(n_) == NOTYPE);
+    _RYML_CB_ASSERT(m_callbacks, (parent(m_) != NONE) || type(m_) == NOTYPE);
+    NodeType tn = type(n_);
+    NodeType tm = type(m_);
+    if(tn != NOTYPE && tm != NOTYPE)
+    {
+        _swap_props(n_, m_);
+        _swap_hierarchy(n_, m_);
+    }
+    else if(tn == NOTYPE && tm != NOTYPE)
+    {
+        _copy_props(n_, m_);
+        _free_list_rem(n_);
+        _copy_hierarchy(n_, m_);
+        _clear(m_);
+        _free_list_add(m_);
+    }
+    else if(tn != NOTYPE && tm == NOTYPE)
+    {
+        _copy_props(m_, n_);
+        _free_list_rem(m_);
+        _copy_hierarchy(m_, n_);
+        _clear(n_);
+        _free_list_add(n_);
+    }
+    else
+    {
+        C4_NEVER_REACH();
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Tree::_swap_hierarchy(size_t ia, size_t ib)
+{
+    if(ia == ib) return;
+
+    for(size_t i = first_child(ia); i != NONE; i = next_sibling(i))
+    {
+        if(i == ib || i == ia)
+            continue;
+        _p(i)->m_parent = ib;
+    }
+
+    for(size_t i = first_child(ib); i != NONE; i = next_sibling(i))
+    {
+        if(i == ib || i == ia)
+            continue;
+        _p(i)->m_parent = ia;
+    }
+
+    auto & C4_RESTRICT a  = *_p(ia);
+    auto & C4_RESTRICT b  = *_p(ib);
+    auto & C4_RESTRICT pa = *_p(a.m_parent);
+    auto & C4_RESTRICT pb = *_p(b.m_parent);
+
+    if(&pa == &pb)
+    {
+        if((pa.m_first_child == ib && pa.m_last_child == ia)
+            ||
+           (pa.m_first_child == ia && pa.m_last_child == ib))
+        {
+            std::swap(pa.m_first_child, pa.m_last_child);
+        }
+        else
+        {
+            bool changed = false;
+            if(pa.m_first_child == ia)
+            {
+                pa.m_first_child = ib;
+                changed = true;
+            }
+            if(pa.m_last_child  == ia)
+            {
+                pa.m_last_child = ib;
+                changed = true;
+            }
+            if(pb.m_first_child == ib && !changed)
+            {
+                pb.m_first_child = ia;
+            }
+            if(pb.m_last_child  == ib && !changed)
+            {
+                pb.m_last_child  = ia;
+            }
+        }
+    }
+    else
+    {
+        if(pa.m_first_child == ia)
+            pa.m_first_child = ib;
+        if(pa.m_last_child  == ia)
+            pa.m_last_child  = ib;
+        if(pb.m_first_child == ib)
+            pb.m_first_child = ia;
+        if(pb.m_last_child  == ib)
+            pb.m_last_child  = ia;
+    }
+    std::swap(a.m_first_child , b.m_first_child);
+    std::swap(a.m_last_child  , b.m_last_child);
+
+    if(a.m_prev_sibling != ib && b.m_prev_sibling != ia &&
+       a.m_next_sibling != ib && b.m_next_sibling != ia)
+    {
+        if(a.m_prev_sibling != NONE && a.m_prev_sibling != ib)
+            _p(a.m_prev_sibling)->m_next_sibling = ib;
+        if(a.m_next_sibling != NONE && a.m_next_sibling != ib)
+            _p(a.m_next_sibling)->m_prev_sibling = ib;
+        if(b.m_prev_sibling != NONE && b.m_prev_sibling != ia)
+            _p(b.m_prev_sibling)->m_next_sibling = ia;
+        if(b.m_next_sibling != NONE && b.m_next_sibling != ia)
+            _p(b.m_next_sibling)->m_prev_sibling = ia;
+        std::swap(a.m_prev_sibling, b.m_prev_sibling);
+        std::swap(a.m_next_sibling, b.m_next_sibling);
+    }
+    else
+    {
+        if(a.m_next_sibling == ib) // n will go after m
+        {
+            _RYML_CB_ASSERT(m_callbacks, b.m_prev_sibling == ia);
+            if(a.m_prev_sibling != NONE)
+            {
+                _RYML_CB_ASSERT(m_callbacks, a.m_prev_sibling != ib);
+                _p(a.m_prev_sibling)->m_next_sibling = ib;
+            }
+            if(b.m_next_sibling != NONE)
+            {
+                _RYML_CB_ASSERT(m_callbacks, b.m_next_sibling != ia);
+                _p(b.m_next_sibling)->m_prev_sibling = ia;
+            }
+            size_t ns = b.m_next_sibling;
+            b.m_prev_sibling = a.m_prev_sibling;
+            b.m_next_sibling = ia;
+            a.m_prev_sibling = ib;
+            a.m_next_sibling = ns;
+        }
+        else if(a.m_prev_sibling == ib) // m will go after n
+        {
+            _RYML_CB_ASSERT(m_callbacks, b.m_next_sibling == ia);
+            if(b.m_prev_sibling != NONE)
+            {
+                _RYML_CB_ASSERT(m_callbacks, b.m_prev_sibling != ia);
+                _p(b.m_prev_sibling)->m_next_sibling = ia;
+            }
+            if(a.m_next_sibling != NONE)
+            {
+                _RYML_CB_ASSERT(m_callbacks, a.m_next_sibling != ib);
+                _p(a.m_next_sibling)->m_prev_sibling = ib;
+            }
+            size_t ns = b.m_prev_sibling;
+            a.m_prev_sibling = b.m_prev_sibling;
+            a.m_next_sibling = ib;
+            b.m_prev_sibling = ia;
+            b.m_next_sibling = ns;
+        }
+        else
+        {
+            C4_NEVER_REACH();
+        }
+    }
+    _RYML_CB_ASSERT(m_callbacks, a.m_next_sibling != ia);
+    _RYML_CB_ASSERT(m_callbacks, a.m_prev_sibling != ia);
+    _RYML_CB_ASSERT(m_callbacks, b.m_next_sibling != ib);
+    _RYML_CB_ASSERT(m_callbacks, b.m_prev_sibling != ib);
+
+    if(a.m_parent != ib && b.m_parent != ia)
+    {
+        std::swap(a.m_parent, b.m_parent);
+    }
+    else
+    {
+        if(a.m_parent == ib && b.m_parent != ia)
+        {
+            a.m_parent = b.m_parent;
+            b.m_parent = ia;
+        }
+        else if(a.m_parent != ib && b.m_parent == ia)
+        {
+            b.m_parent = a.m_parent;
+            a.m_parent = ib;
+        }
+        else
+        {
+            C4_NEVER_REACH();
+        }
+    }
+}
+
+//-----------------------------------------------------------------------------
+void Tree::_copy_hierarchy(size_t dst_, size_t src_)
+{
+    auto const& C4_RESTRICT src = *_p(src_);
+    auto      & C4_RESTRICT dst = *_p(dst_);
+    auto      & C4_RESTRICT prt = *_p(src.m_parent);
+    for(size_t i = src.m_first_child; i != NONE; i = next_sibling(i))
+    {
+        _p(i)->m_parent = dst_;
+    }
+    if(src.m_prev_sibling != NONE)
+    {
+        _p(src.m_prev_sibling)->m_next_sibling = dst_;
+    }
+    if(src.m_next_sibling != NONE)
+    {
+        _p(src.m_next_sibling)->m_prev_sibling = dst_;
+    }
+    if(prt.m_first_child == src_)
+    {
+        prt.m_first_child = dst_;
+    }
+    if(prt.m_last_child  == src_)
+    {
+        prt.m_last_child  = dst_;
+    }
+    dst.m_parent       = src.m_parent;
+    dst.m_first_child  = src.m_first_child;
+    dst.m_last_child   = src.m_last_child;
+    dst.m_prev_sibling = src.m_prev_sibling;
+    dst.m_next_sibling = src.m_next_sibling;
+}
+
+//-----------------------------------------------------------------------------
+void Tree::_swap_props(size_t n_, size_t m_)
+{
+    NodeData &C4_RESTRICT n = *_p(n_);
+    NodeData &C4_RESTRICT m = *_p(m_);
+    std::swap(n.m_type, m.m_type);
+    std::swap(n.m_key, m.m_key);
+    std::swap(n.m_val, m.m_val);
+}
+
+//-----------------------------------------------------------------------------
+void Tree::move(size_t node, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, node != after);
+    _RYML_CB_ASSERT(m_callbacks,  ! is_root(node));
+    _RYML_CB_ASSERT(m_callbacks, (after == NONE) || (has_sibling(node, after) && has_sibling(after, node)));
+
+    _rem_hierarchy(node);
+    _set_hierarchy(node, parent(node), after);
+}
+
+//-----------------------------------------------------------------------------
+
+void Tree::move(size_t node, size_t new_parent, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, node != after);
+    _RYML_CB_ASSERT(m_callbacks, new_parent != NONE);
+    _RYML_CB_ASSERT(m_callbacks, new_parent != node);
+    _RYML_CB_ASSERT(m_callbacks, new_parent != after);
+    _RYML_CB_ASSERT(m_callbacks,  ! is_root(node));
+
+    _rem_hierarchy(node);
+    _set_hierarchy(node, new_parent, after);
+}
+
+size_t Tree::move(Tree *src, size_t node, size_t new_parent, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, src != nullptr);
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, new_parent != NONE);
+    _RYML_CB_ASSERT(m_callbacks, new_parent != after);
+
+    size_t dup = duplicate(src, node, new_parent, after);
+    src->remove(node);
+    return dup;
+}
+
+void Tree::set_root_as_stream()
+{
+    size_t root = root_id();
+    if(is_stream(root))
+        return;
+    // don't use _add_flags() because it's checked and will fail
+    if(!has_children(root))
+    {
+        if(is_val(root))
+        {
+            _p(root)->m_type.add(SEQ);
+            size_t next_doc = append_child(root);
+            _copy_props_wo_key(next_doc, root);
+            _p(next_doc)->m_type.add(DOC);
+            _p(next_doc)->m_type.rem(SEQ);
+        }
+        _p(root)->m_type = STREAM;
+        return;
+    }
+    _RYML_CB_ASSERT(m_callbacks, !has_key(root));
+    size_t next_doc = append_child(root);
+    _copy_props_wo_key(next_doc, root);
+    _add_flags(next_doc, DOC);
+    for(size_t prev = NONE, ch = first_child(root), next = next_sibling(ch); ch != NONE; )
+    {
+        if(ch == next_doc)
+            break;
+        move(ch, next_doc, prev);
+        prev = ch;
+        ch = next;
+        next = next_sibling(next);
+    }
+    _p(root)->m_type = STREAM;
+}
+
+
+//-----------------------------------------------------------------------------
+void Tree::remove_children(size_t node)
+{
+    _RYML_CB_ASSERT(m_callbacks, get(node) != nullptr);
+    size_t ich = get(node)->m_first_child;
+    while(ich != NONE)
+    {
+        remove_children(ich);
+        _RYML_CB_ASSERT(m_callbacks, get(ich) != nullptr);
+        size_t next = get(ich)->m_next_sibling;
+        _release(ich);
+        if(ich == get(node)->m_last_child)
+            break;
+        ich = next;
+    }
+}
+
+bool Tree::change_type(size_t node, NodeType type)
+{
+    _RYML_CB_ASSERT(m_callbacks, type.is_val() || type.is_map() || type.is_seq());
+    _RYML_CB_ASSERT(m_callbacks, type.is_val() + type.is_map() + type.is_seq() == 1);
+    _RYML_CB_ASSERT(m_callbacks, type.has_key() == has_key(node) || (has_key(node) && !type.has_key()));
+    NodeData *d = _p(node);
+    if(type.is_map() && is_map(node))
+        return false;
+    else if(type.is_seq() && is_seq(node))
+        return false;
+    else if(type.is_val() && is_val(node))
+        return false;
+    d->m_type = (d->m_type & (~(MAP|SEQ|VAL))) | type;
+    remove_children(node);
+    return true;
+}
+
+
+//-----------------------------------------------------------------------------
+size_t Tree::duplicate(size_t node, size_t parent, size_t after)
+{
+    return duplicate(this, node, parent, after);
+}
+
+size_t Tree::duplicate(Tree const* src, size_t node, size_t parent, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, src != nullptr);
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, parent != NONE);
+    _RYML_CB_ASSERT(m_callbacks,  ! src->is_root(node));
+
+    size_t copy = _claim();
+
+    _copy_props(copy, src, node);
+    _set_hierarchy(copy, parent, after);
+    duplicate_children(src, node, copy, NONE);
+
+    return copy;
+}
+
+//-----------------------------------------------------------------------------
+size_t Tree::duplicate_children(size_t node, size_t parent, size_t after)
+{
+    return duplicate_children(this, node, parent, after);
+}
+
+size_t Tree::duplicate_children(Tree const* src, size_t node, size_t parent, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, src != nullptr);
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, parent != NONE);
+    _RYML_CB_ASSERT(m_callbacks, after == NONE || has_child(parent, after));
+
+    size_t prev = after;
+    for(size_t i = src->first_child(node); i != NONE; i = src->next_sibling(i))
+    {
+        prev = duplicate(src, i, parent, prev);
+    }
+
+    return prev;
+}
+
+//-----------------------------------------------------------------------------
+void Tree::duplicate_contents(size_t node, size_t where)
+{
+    duplicate_contents(this, node, where);
+}
+
+void Tree::duplicate_contents(Tree const *src, size_t node, size_t where)
+{
+    _RYML_CB_ASSERT(m_callbacks, src != nullptr);
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, where != NONE);
+    _copy_props_wo_key(where, src, node);
+    duplicate_children(src, node, where, last_child(where));
+}
+
+//-----------------------------------------------------------------------------
+size_t Tree::duplicate_children_no_rep(size_t node, size_t parent, size_t after)
+{
+    return duplicate_children_no_rep(this, node, parent, after);
+}
+
+size_t Tree::duplicate_children_no_rep(Tree const *src, size_t node, size_t parent, size_t after)
+{
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, parent != NONE);
+    _RYML_CB_ASSERT(m_callbacks, after == NONE || has_child(parent, after));
+
+    // don't loop using pointers as there may be a relocation
+
+    // find the position where "after" is
+    size_t after_pos = NONE;
+    if(after != NONE)
+    {
+        for(size_t i = first_child(parent), icount = 0; i != NONE; ++icount, i = next_sibling(i))
+        {
+            if(i == after)
+            {
+                after_pos = icount;
+                break;
+            }
+        }
+        _RYML_CB_ASSERT(m_callbacks, after_pos != NONE);
+    }
+
+    // for each child to be duplicated...
+    size_t prev = after;
+    for(size_t i = src->first_child(node), icount = 0; i != NONE; ++icount, i = src->next_sibling(i))
+    {
+        if(is_seq(parent))
+        {
+            prev = duplicate(i, parent, prev);
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_callbacks, is_map(parent));
+            // does the parent already have a node with key equal to that of the current duplicate?
+            size_t rep = NONE, rep_pos = NONE;
+            for(size_t j = first_child(parent), jcount = 0; j != NONE; ++jcount, j = next_sibling(j))
+            {
+                if(key(j) == key(i))
+                {
+                    rep = j;
+                    rep_pos = jcount;
+                    break;
+                }
+            }
+            if(rep == NONE) // there is no repetition; just duplicate
+            {
+                prev = duplicate(src, i, parent, prev);
+            }
+            else  // yes, there is a repetition
+            {
+                if(after_pos != NONE && rep_pos < after_pos)
+                {
+                    // rep is located before the node which will be inserted,
+                    // and will be overridden by the duplicate. So replace it.
+                    remove(rep);
+                    prev = duplicate(src, i, parent, prev);
+                }
+                else if(prev == NONE)
+                {
+                    // first iteration with prev = after = NONE and repetition
+                    prev = rep;
+                }
+                else if(rep != prev)
+                {
+                    // rep is located after the node which will be inserted
+                    // and overrides it. So move the rep into this node's place.
+                    move(rep, prev);
+                    prev = rep;
+                }
+            } // there's a repetition
+        }
+    }
+
+    return prev;
+}
+
+
+//-----------------------------------------------------------------------------
+
+void Tree::merge_with(Tree const *src, size_t src_node, size_t dst_node)
+{
+    _RYML_CB_ASSERT(m_callbacks, src != nullptr);
+    if(src_node == NONE)
+        src_node = src->root_id();
+    if(dst_node == NONE)
+        dst_node = root_id();
+    _RYML_CB_ASSERT(m_callbacks, src->has_val(src_node) || src->is_seq(src_node) || src->is_map(src_node));
+
+    if(src->has_val(src_node))
+    {
+        if( ! has_val(dst_node))
+        {
+            if(has_children(dst_node))
+                remove_children(dst_node);
+        }
+        if(src->is_keyval(src_node))
+            _copy_props(dst_node, src, src_node);
+        else if(src->is_val(src_node))
+            _copy_props_wo_key(dst_node, src, src_node);
+        else
+            C4_NEVER_REACH();
+    }
+    else if(src->is_seq(src_node))
+    {
+        if( ! is_seq(dst_node))
+        {
+            if(has_children(dst_node))
+                remove_children(dst_node);
+            _clear_type(dst_node);
+            if(src->has_key(src_node))
+                to_seq(dst_node, src->key(src_node));
+            else
+                to_seq(dst_node);
+        }
+        for(size_t sch = src->first_child(src_node); sch != NONE; sch = src->next_sibling(sch))
+        {
+            size_t dch = append_child(dst_node);
+            _copy_props_wo_key(dch, src, sch);
+            merge_with(src, sch, dch);
+        }
+    }
+    else if(src->is_map(src_node))
+    {
+        if( ! is_map(dst_node))
+        {
+            if(has_children(dst_node))
+                remove_children(dst_node);
+            _clear_type(dst_node);
+            if(src->has_key(src_node))
+                to_map(dst_node, src->key(src_node));
+            else
+                to_map(dst_node);
+        }
+        for(size_t sch = src->first_child(src_node); sch != NONE; sch = src->next_sibling(sch))
+        {
+            size_t dch = find_child(dst_node, src->key(sch));
+            if(dch == NONE)
+            {
+                dch = append_child(dst_node);
+                _copy_props(dch, src, sch);
+            }
+            merge_with(src, sch, dch);
+        }
+    }
+    else
+    {
+        C4_NEVER_REACH();
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+
+namespace detail {
+/** @todo make this part of the public API, refactoring as appropriate
+ * to be able to use the same resolver to handle multiple trees (one
+ * at a time) */
+struct ReferenceResolver
+{
+    struct refdata
+    {
+        NodeType type;
+        size_t node;
+        size_t prev_anchor;
+        size_t target;
+        size_t parent_ref;
+        size_t parent_ref_sibling;
+    };
+
+    Tree *t;
+    /** from the specs: "an alias node refers to the most recent
+     * node in the serialization having the specified anchor". So
+     * we need to start looking upward from ref nodes.
+     *
+     * @see http://yaml.org/spec/1.2/spec.html#id2765878 */
+    stack<refdata> refs;
+
+    ReferenceResolver(Tree *t_) : t(t_), refs(t_->callbacks())
+    {
+        resolve();
+    }
+
+    void store_anchors_and_refs()
+    {
+        // minimize (re-)allocations by counting first
+        size_t num_anchors_and_refs = count_anchors_and_refs(t->root_id());
+        if(!num_anchors_and_refs)
+            return;
+        refs.reserve(num_anchors_and_refs);
+
+        // now descend through the hierarchy
+        _store_anchors_and_refs(t->root_id());
+
+        // finally connect the reference list
+        size_t prev_anchor = npos;
+        size_t count = 0;
+        for(auto &rd : refs)
+        {
+            rd.prev_anchor = prev_anchor;
+            if(rd.type.is_anchor())
+                prev_anchor = count;
+            ++count;
+        }
+    }
+
+    size_t count_anchors_and_refs(size_t n)
+    {
+        size_t c = 0;
+        c += t->has_key_anchor(n);
+        c += t->has_val_anchor(n);
+        c += t->is_key_ref(n);
+        c += t->is_val_ref(n);
+        for(size_t ch = t->first_child(n); ch != NONE; ch = t->next_sibling(ch))
+            c += count_anchors_and_refs(ch);
+        return c;
+    }
+
+    void _store_anchors_and_refs(size_t n)
+    {
+        if(t->is_key_ref(n) || t->is_val_ref(n) || (t->has_key(n) && t->key(n) == "<<"))
+        {
+            if(t->is_seq(n))
+            {
+                // for merging multiple inheritance targets
+                //   <<: [ *CENTER, *BIG ]
+                for(size_t ich = t->first_child(n); ich != NONE; ich = t->next_sibling(ich))
+                {
+                    RYML_ASSERT(t->num_children(ich) == 0);
+                    refs.push({VALREF, ich, npos, npos, n, t->next_sibling(n)});
+                }
+                return;
+            }
+            if(t->is_key_ref(n) && t->key(n) != "<<") // insert key refs BEFORE inserting val refs
+            {
+                RYML_CHECK((!t->has_key(n)) || t->key(n).ends_with(t->key_ref(n)));
+                refs.push({KEYREF, n, npos, npos, NONE, NONE});
+            }
+            if(t->is_val_ref(n))
+            {
+                RYML_CHECK((!t->has_val(n)) || t->val(n).ends_with(t->val_ref(n)));
+                refs.push({VALREF, n, npos, npos, NONE, NONE});
+            }
+        }
+        if(t->has_key_anchor(n))
+        {
+            RYML_CHECK(t->has_key(n));
+            refs.push({KEYANCH, n, npos, npos, NONE, NONE});
+        }
+        if(t->has_val_anchor(n))
+        {
+            RYML_CHECK(t->has_val(n) || t->is_container(n));
+            refs.push({VALANCH, n, npos, npos, NONE, NONE});
+        }
+        for(size_t ch = t->first_child(n); ch != NONE; ch = t->next_sibling(ch))
+        {
+            _store_anchors_and_refs(ch);
+        }
+    }
+
+    size_t lookup_(refdata *C4_RESTRICT ra)
+    {
+        RYML_ASSERT(ra->type.is_key_ref() || ra->type.is_val_ref());
+        RYML_ASSERT(ra->type.is_key_ref() != ra->type.is_val_ref());
+        csubstr refname;
+        if(ra->type.is_val_ref())
+        {
+            refname = t->val_ref(ra->node);
+        }
+        else
+        {
+            RYML_ASSERT(ra->type.is_key_ref());
+            refname = t->key_ref(ra->node);
+        }
+        while(ra->prev_anchor != npos)
+        {
+            ra = &refs[ra->prev_anchor];
+            if(t->has_anchor(ra->node, refname))
+                return ra->node;
+        }
+
+        #ifndef RYML_ERRMSG_SIZE
+          #define RYML_ERRMSG_SIZE 1024
+        #endif
+
+        char errmsg[RYML_ERRMSG_SIZE];
+        snprintf(errmsg, RYML_ERRMSG_SIZE, "anchor does not exist: '%.*s'",
+                 static_cast<int>(refname.size()), refname.data());
+        c4::yml::error(errmsg);
+        return NONE;
+    }
+
+    void resolve()
+    {
+        store_anchors_and_refs();
+        if(refs.empty())
+            return;
+
+        /* from the specs: "an alias node refers to the most recent
+         * node in the serialization having the specified anchor". So
+         * we need to start looking upward from ref nodes.
+         *
+         * @see http://yaml.org/spec/1.2/spec.html#id2765878 */
+        for(size_t i = 0, e = refs.size(); i < e; ++i)
+        {
+            auto &C4_RESTRICT rd = refs.top(i);
+            if( ! rd.type.is_ref())
+                continue;
+            rd.target = lookup_(&rd);
+        }
+    }
+
+}; // ReferenceResolver
+} // namespace detail
+
+void Tree::resolve()
+{
+    if(m_size == 0)
+        return;
+
+    detail::ReferenceResolver rr(this);
+
+    // insert the resolved references
+    size_t prev_parent_ref = NONE;
+    size_t prev_parent_ref_after = NONE;
+    for(auto const& C4_RESTRICT rd : rr.refs)
+    {
+        if( ! rd.type.is_ref())
+            continue;
+        if(rd.parent_ref != NONE)
+        {
+            _RYML_CB_ASSERT(m_callbacks, is_seq(rd.parent_ref));
+            size_t after, p = parent(rd.parent_ref);
+            if(prev_parent_ref != rd.parent_ref)
+            {
+                after = rd.parent_ref;//prev_sibling(rd.parent_ref_sibling);
+                prev_parent_ref_after = after;
+            }
+            else
+            {
+                after = prev_parent_ref_after;
+            }
+            prev_parent_ref = rd.parent_ref;
+            prev_parent_ref_after = duplicate_children_no_rep(rd.target, p, after);
+            remove(rd.node);
+        }
+        else
+        {
+            if(has_key(rd.node) && is_key_ref(rd.node) && key(rd.node) == "<<")
+            {
+                _RYML_CB_ASSERT(m_callbacks, is_keyval(rd.node));
+                size_t p = parent(rd.node);
+                size_t after = prev_sibling(rd.node);
+                duplicate_children_no_rep(rd.target, p, after);
+                remove(rd.node);
+            }
+            else if(rd.type.is_key_ref())
+            {
+                _RYML_CB_ASSERT(m_callbacks, is_key_ref(rd.node));
+                _RYML_CB_ASSERT(m_callbacks, has_key_anchor(rd.target) || has_val_anchor(rd.target));
+                if(has_val_anchor(rd.target) && val_anchor(rd.target) == key_ref(rd.node))
+                {
+                    _RYML_CB_CHECK(m_callbacks, !is_container(rd.target));
+                    _RYML_CB_CHECK(m_callbacks, has_val(rd.target));
+                    _p(rd.node)->m_key.scalar = val(rd.target);
+                    _add_flags(rd.node, KEY);
+                }
+                else
+                {
+                    _RYML_CB_CHECK(m_callbacks, key_anchor(rd.target) == key_ref(rd.node));
+                    _p(rd.node)->m_key.scalar = key(rd.target);
+                    _add_flags(rd.node, VAL);
+                }
+            }
+            else
+            {
+                _RYML_CB_ASSERT(m_callbacks, rd.type.is_val_ref());
+                if(has_key_anchor(rd.target) && key_anchor(rd.target) == val_ref(rd.node))
+                {
+                    _RYML_CB_CHECK(m_callbacks, !is_container(rd.target));
+                    _RYML_CB_CHECK(m_callbacks, has_val(rd.target));
+                    _p(rd.node)->m_val.scalar = key(rd.target);
+                    _add_flags(rd.node, VAL);
+                }
+                else
+                {
+                    duplicate_contents(rd.target, rd.node);
+                }
+            }
+        }
+    }
+
+    // clear anchors and refs
+    for(auto const& C4_RESTRICT ar : rr.refs)
+    {
+        rem_anchor_ref(ar.node);
+        if(ar.parent_ref != NONE)
+            if(type(ar.parent_ref) != NOTYPE)
+                remove(ar.parent_ref);
+    }
+
+}
+
+//-----------------------------------------------------------------------------
+
+size_t Tree::num_children(size_t node) const
+{
+    size_t count = 0;
+    for(size_t i = first_child(node); i != NONE; i = next_sibling(i))
+        ++count;
+    return count;
+}
+
+size_t Tree::child(size_t node, size_t pos) const
+{
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    size_t count = 0;
+    for(size_t i = first_child(node); i != NONE; i = next_sibling(i))
+    {
+        if(count++ == pos)
+            return i;
+    }
+    return NONE;
+}
+
+size_t Tree::child_pos(size_t node, size_t ch) const
+{
+    size_t count = 0;
+    for(size_t i = first_child(node); i != NONE; i = next_sibling(i))
+    {
+        if(i == ch)
+            return count;
+        ++count;
+    }
+    return npos;
+}
+
+#if defined(__clang__)
+#   pragma clang diagnostic push
+#   pragma GCC diagnostic ignored "-Wnull-dereference"
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic push
+#   if __GNUC__ >= 6
+#       pragma GCC diagnostic ignored "-Wnull-dereference"
+#   endif
+#endif
+
+size_t Tree::find_child(size_t node, csubstr const& name) const
+{
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    _RYML_CB_ASSERT(m_callbacks, is_map(node));
+    if(get(node)->m_first_child == NONE)
+    {
+        _RYML_CB_ASSERT(m_callbacks, _p(node)->m_last_child == NONE);
+        return NONE;
+    }
+    else
+    {
+        _RYML_CB_ASSERT(m_callbacks, _p(node)->m_last_child != NONE);
+    }
+    for(size_t i = first_child(node); i != NONE; i = next_sibling(i))
+    {
+        if(_p(i)->m_key.scalar == name)
+        {
+            return i;
+        }
+    }
+    return NONE;
+}
+
+#if defined(__clang__)
+#   pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#   pragma GCC diagnostic pop
+#endif
+
+
+//-----------------------------------------------------------------------------
+
+void Tree::to_val(size_t node, csubstr val, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || ! parent_is_map(node));
+    _set_flags(node, VAL|more_flags);
+    _p(node)->m_key.clear();
+    _p(node)->m_val = val;
+}
+
+void Tree::to_keyval(size_t node, csubstr key, csubstr val, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || parent_is_map(node));
+    _set_flags(node, KEYVAL|more_flags);
+    _p(node)->m_key = key;
+    _p(node)->m_val = val;
+}
+
+void Tree::to_map(size_t node, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || ! parent_is_map(node)); // parent must not have children with keys
+    _set_flags(node, MAP|more_flags);
+    _p(node)->m_key.clear();
+    _p(node)->m_val.clear();
+}
+
+void Tree::to_map(size_t node, csubstr key, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || parent_is_map(node));
+    _set_flags(node, KEY|MAP|more_flags);
+    _p(node)->m_key = key;
+    _p(node)->m_val.clear();
+}
+
+void Tree::to_seq(size_t node, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || parent_is_seq(node));
+    _set_flags(node, SEQ|more_flags);
+    _p(node)->m_key.clear();
+    _p(node)->m_val.clear();
+}
+
+void Tree::to_seq(size_t node, csubstr key, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _RYML_CB_ASSERT(m_callbacks, parent(node) == NONE || parent_is_map(node));
+    _set_flags(node, KEY|SEQ|more_flags);
+    _p(node)->m_key = key;
+    _p(node)->m_val.clear();
+}
+
+void Tree::to_doc(size_t node, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _set_flags(node, DOC|more_flags);
+    _p(node)->m_key.clear();
+    _p(node)->m_val.clear();
+}
+
+void Tree::to_stream(size_t node, type_bits more_flags)
+{
+    _RYML_CB_ASSERT(m_callbacks,  ! has_children(node));
+    _set_flags(node, STREAM|more_flags);
+    _p(node)->m_key.clear();
+    _p(node)->m_val.clear();
+}
+
+
+//-----------------------------------------------------------------------------
+size_t Tree::num_tag_directives() const
+{
+    // this assumes we have a very small number of tag directives
+    for(size_t i = 0; i < RYML_MAX_TAG_DIRECTIVES; ++i)
+        if(m_tag_directives[i].handle.empty())
+            return i;
+    return RYML_MAX_TAG_DIRECTIVES;
+}
+
+void Tree::clear_tag_directives()
+{
+    for(TagDirective &td : m_tag_directives)
+        td = {};
+}
+
+size_t Tree::add_tag_directive(TagDirective const& td)
+{
+    _RYML_CB_CHECK(m_callbacks, !td.handle.empty());
+    _RYML_CB_CHECK(m_callbacks, !td.prefix.empty());
+    _RYML_CB_ASSERT(m_callbacks, td.handle.begins_with('!'));
+    _RYML_CB_ASSERT(m_callbacks, td.handle.ends_with('!'));
+    // https://yaml.org/spec/1.2.2/#rule-ns-word-char
+    _RYML_CB_ASSERT(m_callbacks, td.handle == '!' || td.handle == "!!" || td.handle.trim('!').first_not_of("01234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-") == npos);
+    size_t pos = num_tag_directives();
+    _RYML_CB_CHECK(m_callbacks, pos < RYML_MAX_TAG_DIRECTIVES);
+    m_tag_directives[pos] = td;
+    return pos;
+}
+
+size_t Tree::resolve_tag(substr output, csubstr tag, size_t node_id) const
+{
+    // lookup from the end. We want to find the first directive that
+    // matches the tag and has a target node id leq than the given
+    // node_id.
+    for(size_t i = RYML_MAX_TAG_DIRECTIVES-1; i != (size_t)-1; --i)
+    {
+        auto const& td = m_tag_directives[i];
+        if(td.handle.empty())
+            continue;
+        if(tag.begins_with(td.handle) && td.next_node_id <= node_id)
+        {
+            _RYML_CB_ASSERT(m_callbacks, tag.len >= td.handle.len);
+            csubstr rest = tag.sub(td.handle.len);
+            size_t len = 1u + td.prefix.len + rest.len + 1u;
+            size_t numpc = rest.count('%');
+            if(numpc == 0)
+            {
+                if(len <= output.len)
+                {
+                    output.str[0] = '<';
+                    memcpy(1u + output.str, td.prefix.str, td.prefix.len);
+                    memcpy(1u + output.str + td.prefix.len, rest.str, rest.len);
+                    output.str[1u + td.prefix.len + rest.len] = '>';
+                }
+            }
+            else
+            {
+                // need to decode URI % sequences
+                size_t pos = rest.find('%');
+                _RYML_CB_ASSERT(m_callbacks, pos != npos);
+                do {
+                    size_t next = rest.first_not_of("0123456789abcdefABCDEF", pos+1);
+                    if(next == npos)
+                        next = rest.len;
+                    _RYML_CB_CHECK(m_callbacks, pos+1 < next);
+                    _RYML_CB_CHECK(m_callbacks, pos+1 + 2 <= next);
+                    size_t delta = next - (pos+1);
+                    len -= delta;
+                    pos = rest.find('%', pos+1);
+                } while(pos != npos);
+                if(len <= output.len)
+                {
+                    size_t prev = 0, wpos = 0;
+                    auto appendstr = [&](csubstr s) { memcpy(output.str + wpos, s.str, s.len); wpos += s.len; };
+                    auto appendchar = [&](char c) { output.str[wpos++] = c; };
+                    appendchar('<');
+                    appendstr(td.prefix);
+                    pos = rest.find('%');
+                    _RYML_CB_ASSERT(m_callbacks, pos != npos);
+                    do {
+                        size_t next = rest.first_not_of("0123456789abcdefABCDEF", pos+1);
+                        if(next == npos)
+                            next = rest.len;
+                        _RYML_CB_CHECK(m_callbacks, pos+1 < next);
+                        _RYML_CB_CHECK(m_callbacks, pos+1 + 2 <= next);
+                        uint8_t val;
+                        if(C4_UNLIKELY(!read_hex(rest.range(pos+1, next), &val) || val > 127))
+                            _RYML_CB_ERR(m_callbacks, "invalid URI character");
+                        appendstr(rest.range(prev, pos));
+                        appendchar((char)val);
+                        prev = next;
+                        pos = rest.find('%', pos+1);
+                    } while(pos != npos);
+                    _RYML_CB_ASSERT(m_callbacks, pos == npos);
+                    _RYML_CB_ASSERT(m_callbacks, prev > 0);
+                    _RYML_CB_ASSERT(m_callbacks, rest.len >= prev);
+                    appendstr(rest.sub(prev));
+                    appendchar('>');
+                    _RYML_CB_ASSERT(m_callbacks, wpos == len);
+                }
+            }
+            return len;
+        }
+    }
+    return 0; // return 0 to signal that the tag is local and cannot be resolved
+}
+
+namespace {
+csubstr _transform_tag(Tree *t, csubstr tag, size_t node)
+{
+    size_t required_size = t->resolve_tag(substr{}, tag, node);
+    if(!required_size)
+        return tag;
+    const char *prev_arena = t->arena().str;
+    substr buf = t->alloc_arena(required_size);
+    _RYML_CB_ASSERT(t->m_callbacks, t->arena().str == prev_arena);
+    size_t actual_size = t->resolve_tag(buf, tag, node);
+    _RYML_CB_ASSERT(t->m_callbacks, actual_size <= required_size);
+    return buf.first(actual_size);
+}
+void _resolve_tags(Tree *t, size_t node)
+{
+    for(size_t child = t->first_child(node); child != NONE; child = t->next_sibling(child))
+    {
+        if(t->has_key(child) && t->has_key_tag(child))
+            t->set_key_tag(child, _transform_tag(t, t->key_tag(child), child));
+        if(t->has_val(child) && t->has_val_tag(child))
+            t->set_val_tag(child, _transform_tag(t, t->val_tag(child), child));
+        _resolve_tags(t, child);
+    }
+}
+size_t _count_resolved_tags_size(Tree const* t, size_t node)
+{
+    size_t sz = 0;
+    for(size_t child = t->first_child(node); child != NONE; child = t->next_sibling(child))
+    {
+        if(t->has_key(child) && t->has_key_tag(child))
+            sz += t->resolve_tag(substr{}, t->key_tag(child), child);
+        if(t->has_val(child) && t->has_val_tag(child))
+            sz += t->resolve_tag(substr{}, t->val_tag(child), child);
+        sz += _count_resolved_tags_size(t, child);
+    }
+    return sz;
+}
+} // namespace
+
+void Tree::resolve_tags()
+{
+    if(empty())
+        return;
+    if(num_tag_directives() == 0)
+        return;
+    size_t needed_size = _count_resolved_tags_size(this, root_id());
+    if(needed_size)
+        reserve_arena(arena_size() + needed_size);
+    _resolve_tags(this, root_id());
+}
+
+
+//-----------------------------------------------------------------------------
+
+csubstr Tree::lookup_result::resolved() const
+{
+    csubstr p = path.first(path_pos);
+    if(p.ends_with('.'))
+        p = p.first(p.len-1);
+    return p;
+}
+
+csubstr Tree::lookup_result::unresolved() const
+{
+    return path.sub(path_pos);
+}
+
+void Tree::_advance(lookup_result *r, size_t more) const
+{
+    r->path_pos += more;
+    if(r->path.sub(r->path_pos).begins_with('.'))
+        ++r->path_pos;
+}
+
+Tree::lookup_result Tree::lookup_path(csubstr path, size_t start) const
+{
+    if(start == NONE)
+        start = root_id();
+    lookup_result r(path, start);
+    if(path.empty())
+        return r;
+    _lookup_path(&r);
+    if(r.target == NONE && r.closest == start)
+        r.closest = NONE;
+    return r;
+}
+
+size_t Tree::lookup_path_or_modify(csubstr default_value, csubstr path, size_t start)
+{
+    size_t target = _lookup_path_or_create(path, start);
+    if(parent_is_map(target))
+        to_keyval(target, key(target), default_value);
+    else
+        to_val(target, default_value);
+    return target;
+}
+
+size_t Tree::lookup_path_or_modify(Tree const *src, size_t src_node, csubstr path, size_t start)
+{
+    size_t target = _lookup_path_or_create(path, start);
+    merge_with(src, src_node, target);
+    return target;
+}
+
+size_t Tree::_lookup_path_or_create(csubstr path, size_t start)
+{
+    if(start == NONE)
+        start = root_id();
+    lookup_result r(path, start);
+    _lookup_path(&r);
+    if(r.target != NONE)
+    {
+        C4_ASSERT(r.unresolved().empty());
+        return r.target;
+    }
+    _lookup_path_modify(&r);
+    return r.target;
+}
+
+void Tree::_lookup_path(lookup_result *r) const
+{
+    C4_ASSERT( ! r->unresolved().empty());
+    _lookup_path_token parent{"", type(r->closest)};
+    size_t node;
+    do
+    {
+        node = _next_node(r, &parent);
+        if(node != NONE)
+            r->closest = node;
+        if(r->unresolved().empty())
+        {
+            r->target = node;
+            return;
+        }
+    } while(node != NONE);
+}
+
+void Tree::_lookup_path_modify(lookup_result *r)
+{
+    C4_ASSERT( ! r->unresolved().empty());
+    _lookup_path_token parent{"", type(r->closest)};
+    size_t node;
+    do
+    {
+        node = _next_node_modify(r, &parent);
+        if(node != NONE)
+            r->closest = node;
+        if(r->unresolved().empty())
+        {
+            r->target = node;
+            return;
+        }
+    } while(node != NONE);
+}
+
+size_t Tree::_next_node(lookup_result * r, _lookup_path_token *parent) const
+{
+    _lookup_path_token token = _next_token(r, *parent);
+    if( ! token)
+        return NONE;
+
+    size_t node = NONE;
+    csubstr prev = token.value;
+    if(token.type == MAP || token.type == SEQ)
+    {
+        _RYML_CB_ASSERT(m_callbacks, !token.value.begins_with('['));
+        //_RYML_CB_ASSERT(m_callbacks, is_container(r->closest) || r->closest == NONE);
+        _RYML_CB_ASSERT(m_callbacks, is_map(r->closest));
+        node = find_child(r->closest, token.value);
+    }
+    else if(token.type == KEYVAL)
+    {
+        _RYML_CB_ASSERT(m_callbacks, r->unresolved().empty());
+        if(is_map(r->closest))
+            node = find_child(r->closest, token.value);
+    }
+    else if(token.type == KEY)
+    {
+        _RYML_CB_ASSERT(m_callbacks, token.value.begins_with('[') && token.value.ends_with(']'));
+        token.value = token.value.offs(1, 1).trim(' ');
+        size_t idx = 0;
+        _RYML_CB_CHECK(m_callbacks, from_chars(token.value, &idx));
+        node = child(r->closest, idx);
+    }
+    else
+    {
+        C4_NEVER_REACH();
+    }
+
+    if(node != NONE)
+    {
+        *parent = token;
+    }
+    else
+    {
+        csubstr p = r->path.sub(r->path_pos > 0 ? r->path_pos - 1 : r->path_pos);
+        r->path_pos -= prev.len;
+        if(p.begins_with('.'))
+            r->path_pos -= 1u;
+    }
+
+    return node;
+}
+
+size_t Tree::_next_node_modify(lookup_result * r, _lookup_path_token *parent)
+{
+    _lookup_path_token token = _next_token(r, *parent);
+    if( ! token)
+        return NONE;
+
+    size_t node = NONE;
+    if(token.type == MAP || token.type == SEQ)
+    {
+        _RYML_CB_ASSERT(m_callbacks, !token.value.begins_with('['));
+        //_RYML_CB_ASSERT(m_callbacks, is_container(r->closest) || r->closest == NONE);
+        if( ! is_container(r->closest))
+        {
+            if(has_key(r->closest))
+                to_map(r->closest, key(r->closest));
+            else
+                to_map(r->closest);
+        }
+        else
+        {
+            if(is_map(r->closest))
+                node = find_child(r->closest, token.value);
+            else
+            {
+                size_t pos = NONE;
+                _RYML_CB_CHECK(m_callbacks, c4::atox(token.value, &pos));
+                _RYML_CB_ASSERT(m_callbacks, pos != NONE);
+                node = child(r->closest, pos);
+            }
+        }
+        if(node == NONE)
+        {
+            _RYML_CB_ASSERT(m_callbacks, is_map(r->closest));
+            node = append_child(r->closest);
+            NodeData *n = _p(node);
+            n->m_key.scalar = token.value;
+            n->m_type.add(KEY);
+        }
+    }
+    else if(token.type == KEYVAL)
+    {
+        _RYML_CB_ASSERT(m_callbacks, r->unresolved().empty());
+        if(is_map(r->closest))
+        {
+            node = find_child(r->closest, token.value);
+            if(node == NONE)
+                node = append_child(r->closest);
+        }
+        else
+        {
+            _RYML_CB_ASSERT(m_callbacks, !is_seq(r->closest));
+            _add_flags(r->closest, MAP);
+            node = append_child(r->closest);
+        }
+        NodeData *n = _p(node);
+        n->m_key.scalar = token.value;
+        n->m_val.scalar = "";
+        n->m_type.add(KEYVAL);
+    }
+    else if(token.type == KEY)
+    {
+        _RYML_CB_ASSERT(m_callbacks, token.value.begins_with('[') && token.value.ends_with(']'));
+        token.value = token.value.offs(1, 1).trim(' ');
+        size_t idx;
+        if( ! from_chars(token.value, &idx))
+             return NONE;
+        if( ! is_container(r->closest))
+        {
+            if(has_key(r->closest))
+            {
+                csubstr k = key(r->closest);
+                _clear_type(r->closest);
+                to_seq(r->closest, k);
+            }
+            else
+            {
+                _clear_type(r->closest);
+                to_seq(r->closest);
+            }
+        }
+        _RYML_CB_ASSERT(m_callbacks, is_container(r->closest));
+        node = child(r->closest, idx);
+        if(node == NONE)
+        {
+            _RYML_CB_ASSERT(m_callbacks, num_children(r->closest) <= idx);
+            for(size_t i = num_children(r->closest); i <= idx; ++i)
+            {
+                node = append_child(r->closest);
+                if(i < idx)
+                {
+                    if(is_map(r->closest))
+                        to_keyval(node, /*"~"*/{}, /*"~"*/{});
+                    else if(is_seq(r->closest))
+                        to_val(node, /*"~"*/{});
+                }
+            }
+        }
+    }
+    else
+    {
+        C4_NEVER_REACH();
+    }
+
+    _RYML_CB_ASSERT(m_callbacks, node != NONE);
+    *parent = token;
+    return node;
+}
+
+/** types of tokens:
+ * - seeing "map."  ---> "map"/MAP
+ * - finishing "scalar" ---> "scalar"/KEYVAL
+ * - seeing "seq[n]" ---> "seq"/SEQ (--> "[n]"/KEY)
+ * - seeing "[n]" ---> "[n]"/KEY
+ */
+Tree::_lookup_path_token Tree::_next_token(lookup_result *r, _lookup_path_token const& parent) const
+{
+    csubstr unres = r->unresolved();
+    if(unres.empty())
+        return {};
+
+    // is it an indexation like [0], [1], etc?
+    if(unres.begins_with('['))
+    {
+        size_t pos = unres.find(']');
+        if(pos == csubstr::npos)
+            return {};
+        csubstr idx = unres.first(pos + 1);
+        _advance(r, pos + 1);
+        return {idx, KEY};
+    }
+
+    // no. so it must be a name
+    size_t pos = unres.first_of(".[");
+    if(pos == csubstr::npos)
+    {
+        _advance(r, unres.len);
+        NodeType t;
+        if(( ! parent) || parent.type.is_seq())
+            return {unres, VAL};
+        return {unres, KEYVAL};
+    }
+
+    // it's either a map or a seq
+    _RYML_CB_ASSERT(m_callbacks, unres[pos] == '.' || unres[pos] == '[');
+    if(unres[pos] == '.')
+    {
+        _RYML_CB_ASSERT(m_callbacks, pos != 0);
+        _advance(r, pos + 1);
+        return {unres.first(pos), MAP};
+    }
+
+    _RYML_CB_ASSERT(m_callbacks, unres[pos] == '[');
+    _advance(r, pos);
+    return {unres.first(pos), SEQ};
+}
+
+
+} // namespace ryml
+} // namespace c4
+
+
+C4_SUPPRESS_WARNING_GCC_POP
+C4_SUPPRESS_WARNING_MSVC_POP
diff --git a/thirdparty/ryml/src/c4/yml/tree.hpp b/thirdparty/ryml/src/c4/yml/tree.hpp
new file mode 100644
index 000000000..5adc5583a
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/tree.hpp
@@ -0,0 +1,1495 @@
+#ifndef _C4_YML_TREE_HPP_
+#define _C4_YML_TREE_HPP_
+
+
+#include "c4/error.hpp"
+#include "c4/types.hpp"
+#ifndef _C4_YML_COMMON_HPP_
+#include "c4/yml/common.hpp"
+#endif
+
+#include <c4/charconv.hpp>
+#include <cmath>
+#include <limits>
+
+
+C4_SUPPRESS_WARNING_MSVC_PUSH
+C4_SUPPRESS_WARNING_MSVC(4251) // needs to have dll-interface to be used by clients of struct
+C4_SUPPRESS_WARNING_MSVC(4296) // expression is always 'boolean_value'
+C4_SUPPRESS_WARNING_GCC_CLANG_PUSH
+C4_SUPPRESS_WARNING_GCC("-Wtype-limits")
+
+
+namespace c4 {
+namespace yml {
+
+struct NodeScalar;
+struct NodeInit;
+struct NodeData;
+class NodeRef;
+class ConstNodeRef;
+class Tree;
+
+
+/** encode a floating point value to a string. */
+template<class T>
+size_t to_chars_float(substr buf, T val)
+{
+    C4_SUPPRESS_WARNING_GCC_CLANG_WITH_PUSH("-Wfloat-equal");
+    static_assert(std::is_floating_point<T>::value, "must be floating point");
+    if(C4_UNLIKELY(std::isnan(val)))
+        return to_chars(buf, csubstr(".nan"));
+    else if(C4_UNLIKELY(val == std::numeric_limits<T>::infinity()))
+        return to_chars(buf, csubstr(".inf"));
+    else if(C4_UNLIKELY(val == -std::numeric_limits<T>::infinity()))
+        return to_chars(buf, csubstr("-.inf"));
+    return to_chars(buf, val);
+    C4_SUPPRESS_WARNING_GCC_CLANG_POP
+}
+
+
+/** decode a floating point from string. Accepts special values: .nan,
+ * .inf, -.inf */
+template<class T>
+bool from_chars_float(csubstr buf, T *C4_RESTRICT val)
+{
+    static_assert(std::is_floating_point<T>::value, "must be floating point");
+    if(C4_LIKELY(from_chars(buf, val)))
+    {
+        return true;
+    }
+    else if(C4_UNLIKELY(buf == ".nan" || buf == ".NaN" || buf == ".NAN"))
+    {
+        *val = std::numeric_limits<T>::quiet_NaN();
+        return true;
+    }
+    else if(C4_UNLIKELY(buf == ".inf" || buf == ".Inf" || buf == ".INF"))
+    {
+        *val = std::numeric_limits<T>::infinity();
+        return true;
+    }
+    else if(C4_UNLIKELY(buf == "-.inf" || buf == "-.Inf" || buf == "-.INF"))
+    {
+        *val = -std::numeric_limits<T>::infinity();
+        return true;
+    }
+    else
+    {
+        return false;
+    }
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** the integral type necessary to cover all the bits marking node tags */
+using tag_bits = uint16_t;
+
+/** a bit mask for marking tags for types */
+typedef enum : tag_bits {
+    // container types
+    TAG_NONE      =  0,
+    TAG_MAP       =  1, /**< !!map   Unordered set of key: value pairs without duplicates. @see https://yaml.org/type/map.html */
+    TAG_OMAP      =  2, /**< !!omap  Ordered sequence of key: value pairs without duplicates. @see https://yaml.org/type/omap.html */
+    TAG_PAIRS     =  3, /**< !!pairs Ordered sequence of key: value pairs allowing duplicates. @see https://yaml.org/type/pairs.html */
+    TAG_SET       =  4, /**< !!set   Unordered set of non-equal values. @see https://yaml.org/type/set.html */
+    TAG_SEQ       =  5, /**< !!seq   Sequence of arbitrary values. @see https://yaml.org/type/seq.html */
+    // scalar types
+    TAG_BINARY    =  6, /**< !!binary A sequence of zero or more octets (8 bit values). @see https://yaml.org/type/binary.html */
+    TAG_BOOL      =  7, /**< !!bool   Mathematical Booleans. @see https://yaml.org/type/bool.html */
+    TAG_FLOAT     =  8, /**< !!float  Floating-point approximation to real numbers. https://yaml.org/type/float.html */
+    TAG_INT       =  9, /**< !!float  Mathematical integers. https://yaml.org/type/int.html */
+    TAG_MERGE     = 10, /**< !!merge  Specify one or more mapping to be merged with the current one. https://yaml.org/type/merge.html */
+    TAG_NULL      = 11, /**< !!null   Devoid of value. https://yaml.org/type/null.html */
+    TAG_STR       = 12, /**< !!str    A sequence of zero or more Unicode characters. https://yaml.org/type/str.html */
+    TAG_TIMESTAMP = 13, /**< !!timestamp A point in time https://yaml.org/type/timestamp.html */
+    TAG_VALUE     = 14, /**< !!value  Specify the default value of a mapping https://yaml.org/type/value.html */
+    TAG_YAML      = 15, /**< !!yaml   Specify the default value of a mapping https://yaml.org/type/yaml.html */
+} YamlTag_e;
+
+YamlTag_e to_tag(csubstr tag);
+csubstr from_tag(YamlTag_e tag);
+csubstr from_tag_long(YamlTag_e tag);
+csubstr normalize_tag(csubstr tag);
+csubstr normalize_tag_long(csubstr tag);
+
+struct TagDirective
+{
+    /** Eg `!e!` in `%TAG !e! tag:example.com,2000:app/` */
+    csubstr handle;
+    /** Eg `tag:example.com,2000:app/` in `%TAG !e! tag:example.com,2000:app/` */
+    csubstr prefix;
+    /** The next node to which this tag directive applies */
+    size_t next_node_id;
+};
+
+#ifndef RYML_MAX_TAG_DIRECTIVES
+/** the maximum number of tag directives in a Tree */
+#define RYML_MAX_TAG_DIRECTIVES 4
+#endif
+
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+
+/** the integral type necessary to cover all the bits marking node types */
+using type_bits = uint64_t;
+
+
+/** a bit mask for marking node types */
+typedef enum : type_bits {
+    // a convenience define, undefined below
+    #define c4bit(v) (type_bits(1) << v)
+    NOTYPE  = 0,            ///< no node type is set
+    VAL     = c4bit(0),     ///< a leaf node, has a (possibly empty) value
+    KEY     = c4bit(1),     ///< is member of a map, must have non-empty key
+    MAP     = c4bit(2),     ///< a map: a parent of keyvals
+    SEQ     = c4bit(3),     ///< a seq: a parent of vals
+    DOC     = c4bit(4),     ///< a document
+    STREAM  = c4bit(5)|SEQ, ///< a stream: a seq of docs
+    KEYREF  = c4bit(6),     ///< a *reference: the key references an &anchor
+    VALREF  = c4bit(7),     ///< a *reference: the val references an &anchor
+    KEYANCH = c4bit(8),     ///< the key has an &anchor
+    VALANCH = c4bit(9),     ///< the val has an &anchor
+    KEYTAG  = c4bit(10),    ///< the key has an explicit tag/type
+    VALTAG  = c4bit(11),    ///< the val has an explicit tag/type
+    _TYMASK = c4bit(12)-1,  // all the bits up to here
+    VALQUO  = c4bit(12),    ///< the val is quoted by '', "", > or |
+    KEYQUO  = c4bit(13),    ///< the key is quoted by '', "", > or |
+    KEYVAL  = KEY|VAL,
+    KEYSEQ  = KEY|SEQ,
+    KEYMAP  = KEY|MAP,
+    DOCMAP  = DOC|MAP,
+    DOCSEQ  = DOC|SEQ,
+    DOCVAL  = DOC|VAL,
+    _KEYMASK = KEY | KEYQUO | KEYANCH | KEYREF | KEYTAG,
+    _VALMASK = VAL | VALQUO | VALANCH | VALREF | VALTAG,
+    // these flags are from a work in progress and should not be used yet
+    _WIP_STYLE_FLOW_SL = c4bit(14), ///< mark container with single-line flow format (seqs as '[val1,val2], maps as '{key: val, key2: val2}')
+    _WIP_STYLE_FLOW_ML = c4bit(15), ///< mark container with multi-line flow format (seqs as '[val1,\nval2], maps as '{key: val,\nkey2: val2}')
+    _WIP_STYLE_BLOCK   = c4bit(16), ///< mark container with block format (seqs as '- val\n', maps as 'key: val')
+    _WIP_KEY_LITERAL   = c4bit(17), ///< mark key scalar as multiline, block literal |
+    _WIP_VAL_LITERAL   = c4bit(18), ///< mark val scalar as multiline, block literal |
+    _WIP_KEY_FOLDED    = c4bit(19), ///< mark key scalar as multiline, block folded >
+    _WIP_VAL_FOLDED    = c4bit(20), ///< mark val scalar as multiline, block folded >
+    _WIP_KEY_SQUO      = c4bit(21), ///< mark key scalar as single quoted
+    _WIP_VAL_SQUO      = c4bit(22), ///< mark val scalar as single quoted
+    _WIP_KEY_DQUO      = c4bit(23), ///< mark key scalar as double quoted
+    _WIP_VAL_DQUO      = c4bit(24), ///< mark val scalar as double quoted
+    _WIP_KEY_PLAIN     = c4bit(25), ///< mark key scalar as plain scalar (unquoted, even when multiline)
+    _WIP_VAL_PLAIN     = c4bit(26), ///< mark val scalar as plain scalar (unquoted, even when multiline)
+    _WIP_KEY_STYLE     = _WIP_KEY_LITERAL|_WIP_KEY_FOLDED|_WIP_KEY_SQUO|_WIP_KEY_DQUO|_WIP_KEY_PLAIN,
+    _WIP_VAL_STYLE     = _WIP_VAL_LITERAL|_WIP_VAL_FOLDED|_WIP_VAL_SQUO|_WIP_VAL_DQUO|_WIP_VAL_PLAIN,
+    _WIP_KEY_FT_NL     = c4bit(27), ///< features: mark key scalar as having \n in its contents
+    _WIP_VAL_FT_NL     = c4bit(28), ///< features: mark val scalar as having \n in its contents
+    _WIP_KEY_FT_SQ     = c4bit(29), ///< features: mark key scalar as having single quotes in its contents
+    _WIP_VAL_FT_SQ     = c4bit(30), ///< features: mark val scalar as having single quotes in its contents
+    _WIP_KEY_FT_DQ     = c4bit(31), ///< features: mark key scalar as having double quotes in its contents
+    _WIP_VAL_FT_DQ     = c4bit(32), ///< features: mark val scalar as having double quotes in its contents
+    #undef c4bit
+} NodeType_e;
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** wraps a NodeType_e element with some syntactic sugar and predicates */
+struct NodeType
+{
+public:
+
+    NodeType_e type;
+
+public:
+
+    C4_ALWAYS_INLINE NodeType() : type(NOTYPE) {}
+    C4_ALWAYS_INLINE NodeType(NodeType_e t) : type(t) {}
+    C4_ALWAYS_INLINE NodeType(type_bits t) : type((NodeType_e)t) {}
+
+    C4_ALWAYS_INLINE const char *type_str() const { return type_str(type); }
+    static const char* type_str(NodeType_e t);
+
+    C4_ALWAYS_INLINE void set(NodeType_e t) { type = t; }
+    C4_ALWAYS_INLINE void set(type_bits  t) { type = (NodeType_e)t; }
+
+    C4_ALWAYS_INLINE void add(NodeType_e t) { type = (NodeType_e)(type|t); }
+    C4_ALWAYS_INLINE void add(type_bits  t) { type = (NodeType_e)(type|t); }
+
+    C4_ALWAYS_INLINE void rem(NodeType_e t) { type = (NodeType_e)(type & ~t); }
+    C4_ALWAYS_INLINE void rem(type_bits  t) { type = (NodeType_e)(type & ~t); }
+
+    C4_ALWAYS_INLINE void clear() { type = NOTYPE; }
+
+public:
+
+    C4_ALWAYS_INLINE operator NodeType_e      & C4_RESTRICT ()       { return type; }
+    C4_ALWAYS_INLINE operator NodeType_e const& C4_RESTRICT () const { return type; }
+
+    C4_ALWAYS_INLINE bool operator== (NodeType_e t) const { return type == t; }
+    C4_ALWAYS_INLINE bool operator!= (NodeType_e t) const { return type != t; }
+
+public:
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic push
+    #   pragma clang diagnostic ignored "-Wnull-dereference"
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic push
+    #   if __GNUC__ >= 6
+    #       pragma GCC diagnostic ignored "-Wnull-dereference"
+    #   endif
+    #endif
+
+    C4_ALWAYS_INLINE bool is_notype() const { return type == NOTYPE; }
+    C4_ALWAYS_INLINE bool is_stream() const { return ((type & STREAM) == STREAM) != 0; }
+    C4_ALWAYS_INLINE bool is_doc() const { return (type & DOC) != 0; }
+    C4_ALWAYS_INLINE bool is_container() const { return (type & (MAP|SEQ|STREAM)) != 0; }
+    C4_ALWAYS_INLINE bool is_map() const { return (type & MAP) != 0; }
+    C4_ALWAYS_INLINE bool is_seq() const { return (type & SEQ) != 0; }
+    C4_ALWAYS_INLINE bool has_key() const { return (type & KEY) != 0; }
+    C4_ALWAYS_INLINE bool has_val() const { return (type & VAL) != 0; }
+    C4_ALWAYS_INLINE bool is_val() const { return (type & KEYVAL) == VAL; }
+    C4_ALWAYS_INLINE bool is_keyval() const { return (type & KEYVAL) == KEYVAL; }
+    C4_ALWAYS_INLINE bool has_key_tag() const { return (type & (KEY|KEYTAG)) == (KEY|KEYTAG); }
+    C4_ALWAYS_INLINE bool has_val_tag() const { return ((type & VALTAG) && (type & (VAL|MAP|SEQ))); }
+    C4_ALWAYS_INLINE bool has_key_anchor() const { return (type & (KEY|KEYANCH)) == (KEY|KEYANCH); }
+    C4_ALWAYS_INLINE bool is_key_anchor() const { return (type & (KEY|KEYANCH)) == (KEY|KEYANCH); }
+    C4_ALWAYS_INLINE bool has_val_anchor() const { return (type & VALANCH) != 0 && (type & (VAL|SEQ|MAP)) != 0; }
+    C4_ALWAYS_INLINE bool is_val_anchor() const { return (type & VALANCH) != 0 && (type & (VAL|SEQ|MAP)) != 0; }
+    C4_ALWAYS_INLINE bool has_anchor() const { return (type & (KEYANCH|VALANCH)) != 0; }
+    C4_ALWAYS_INLINE bool is_anchor() const { return (type & (KEYANCH|VALANCH)) != 0; }
+    C4_ALWAYS_INLINE bool is_key_ref() const { return (type & KEYREF) != 0; }
+    C4_ALWAYS_INLINE bool is_val_ref() const { return (type & VALREF) != 0; }
+    C4_ALWAYS_INLINE bool is_ref() const { return (type & (KEYREF|VALREF)) != 0; }
+    C4_ALWAYS_INLINE bool is_anchor_or_ref() const { return (type & (KEYANCH|VALANCH|KEYREF|VALREF)) != 0; }
+    C4_ALWAYS_INLINE bool is_key_quoted() const { return (type & (KEY|KEYQUO)) == (KEY|KEYQUO); }
+    C4_ALWAYS_INLINE bool is_val_quoted() const { return (type & (VAL|VALQUO)) == (VAL|VALQUO); }
+    C4_ALWAYS_INLINE bool is_quoted() const { return (type & (KEY|KEYQUO)) == (KEY|KEYQUO) || (type & (VAL|VALQUO)) == (VAL|VALQUO); }
+
+    // these predicates are a work in progress and subject to change. Don't use yet.
+    C4_ALWAYS_INLINE bool default_block() const { return (type & (_WIP_STYLE_BLOCK|_WIP_STYLE_FLOW_ML|_WIP_STYLE_FLOW_SL)) == 0; }
+    C4_ALWAYS_INLINE bool marked_block() const { return (type & (_WIP_STYLE_BLOCK)) != 0; }
+    C4_ALWAYS_INLINE bool marked_flow_sl() const { return (type & (_WIP_STYLE_FLOW_SL)) != 0; }
+    C4_ALWAYS_INLINE bool marked_flow_ml() const { return (type & (_WIP_STYLE_FLOW_ML)) != 0; }
+    C4_ALWAYS_INLINE bool marked_flow() const { return (type & (_WIP_STYLE_FLOW_ML|_WIP_STYLE_FLOW_SL)) != 0; }
+    C4_ALWAYS_INLINE bool key_marked_literal() const { return (type & (_WIP_KEY_LITERAL)) != 0; }
+    C4_ALWAYS_INLINE bool val_marked_literal() const { return (type & (_WIP_VAL_LITERAL)) != 0; }
+    C4_ALWAYS_INLINE bool key_marked_folded() const { return (type & (_WIP_KEY_FOLDED)) != 0; }
+    C4_ALWAYS_INLINE bool val_marked_folded() const { return (type & (_WIP_VAL_FOLDED)) != 0; }
+    C4_ALWAYS_INLINE bool key_marked_squo() const { return (type & (_WIP_KEY_SQUO)) != 0; }
+    C4_ALWAYS_INLINE bool val_marked_squo() const { return (type & (_WIP_VAL_SQUO)) != 0; }
+    C4_ALWAYS_INLINE bool key_marked_dquo() const { return (type & (_WIP_KEY_DQUO)) != 0; }
+    C4_ALWAYS_INLINE bool val_marked_dquo() const { return (type & (_WIP_VAL_DQUO)) != 0; }
+    C4_ALWAYS_INLINE bool key_marked_plain() const { return (type & (_WIP_KEY_PLAIN)) != 0; }
+    C4_ALWAYS_INLINE bool val_marked_plain() const { return (type & (_WIP_VAL_PLAIN)) != 0; }
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic pop
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic pop
+    #endif
+
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** a node scalar is a csubstr, which may be tagged and anchored. */
+struct NodeScalar
+{
+    csubstr tag;
+    csubstr scalar;
+    csubstr anchor;
+
+public:
+
+    /// initialize as an empty scalar
+    inline NodeScalar() noexcept : tag(), scalar(), anchor() {}
+
+    /// initialize as an untagged scalar
+    template<size_t N>
+    inline NodeScalar(const char (&s)[N]) noexcept : tag(), scalar(s), anchor() {}
+    inline NodeScalar(csubstr      s    ) noexcept : tag(), scalar(s), anchor() {}
+
+    /// initialize as a tagged scalar
+    template<size_t N, size_t M>
+    inline NodeScalar(const char (&t)[N], const char (&s)[N]) noexcept : tag(t), scalar(s), anchor() {}
+    inline NodeScalar(csubstr      t    , csubstr      s    ) noexcept : tag(t), scalar(s), anchor() {}
+
+public:
+
+    ~NodeScalar() noexcept = default;
+    NodeScalar(NodeScalar &&) noexcept = default;
+    NodeScalar(NodeScalar const&) noexcept = default;
+    NodeScalar& operator= (NodeScalar &&) noexcept = default;
+    NodeScalar& operator= (NodeScalar const&) noexcept = default;
+
+public:
+
+    bool empty() const noexcept { return tag.empty() && scalar.empty() && anchor.empty(); }
+
+    void clear() noexcept { tag.clear(); scalar.clear(); anchor.clear(); }
+
+    void set_ref_maybe_replacing_scalar(csubstr ref, bool has_scalar) noexcept
+    {
+        csubstr trimmed = ref.begins_with('*') ? ref.sub(1) : ref;
+        anchor = trimmed;
+        if((!has_scalar) || !scalar.ends_with(trimmed))
+            scalar = ref;
+    }
+};
+C4_MUST_BE_TRIVIAL_COPY(NodeScalar);
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** convenience class to initialize nodes */
+struct NodeInit
+{
+
+    NodeType   type;
+    NodeScalar key;
+    NodeScalar val;
+
+public:
+
+    /// initialize as an empty node
+    NodeInit() : type(NOTYPE), key(), val() {}
+    /// initialize as a typed node
+    NodeInit(NodeType_e t) : type(t), key(), val() {}
+    /// initialize as a sequence member
+    NodeInit(NodeScalar const& v) : type(VAL), key(), val(v) { _add_flags(); }
+    /// initialize as a mapping member
+    NodeInit(              NodeScalar const& k, NodeScalar const& v) : type(KEYVAL), key(k.tag, k.scalar), val(v.tag, v.scalar) { _add_flags(); }
+    /// initialize as a mapping member with explicit type
+    NodeInit(NodeType_e t, NodeScalar const& k, NodeScalar const& v) : type(t     ), key(k.tag, k.scalar), val(v.tag, v.scalar) { _add_flags(); }
+    /// initialize as a mapping member with explicit type (eg SEQ or MAP)
+    NodeInit(NodeType_e t, NodeScalar const& k                     ) : type(t     ), key(k.tag, k.scalar), val(               ) { _add_flags(KEY); }
+
+public:
+
+    void clear()
+    {
+        type.clear();
+        key.clear();
+        val.clear();
+    }
+
+    void _add_flags(type_bits more_flags=0)
+    {
+        type = (type|more_flags);
+        if( ! key.tag.empty())
+            type = (type|KEYTAG);
+        if( ! val.tag.empty())
+            type = (type|VALTAG);
+        if( ! key.anchor.empty())
+            type = (type|KEYANCH);
+        if( ! val.anchor.empty())
+            type = (type|VALANCH);
+    }
+
+    bool _check() const
+    {
+        // key cannot be empty
+        RYML_ASSERT(key.scalar.empty() == ((type & KEY) == 0));
+        // key tag cannot be empty
+        RYML_ASSERT(key.tag.empty() == ((type & KEYTAG) == 0));
+        // val may be empty even though VAL is set. But when VAL is not set, val must be empty
+        RYML_ASSERT(((type & VAL) != 0) || val.scalar.empty());
+        // val tag cannot be empty
+        RYML_ASSERT(val.tag.empty() == ((type & VALTAG) == 0));
+        return true;
+    }
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+/** contains the data for each YAML node. */
+struct NodeData
+{
+    NodeType   m_type;
+
+    NodeScalar m_key;
+    NodeScalar m_val;
+
+    size_t     m_parent;
+    size_t     m_first_child;
+    size_t     m_last_child;
+    size_t     m_next_sibling;
+    size_t     m_prev_sibling;
+};
+C4_MUST_BE_TRIVIAL_COPY(NodeData);
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+
+class RYML_EXPORT Tree
+{
+public:
+
+    /** @name construction and assignment */
+    /** @{ */
+
+    Tree() : Tree(get_callbacks()) {}
+    Tree(Callbacks const& cb);
+    Tree(size_t node_capacity, size_t arena_capacity=0) : Tree(node_capacity, arena_capacity, get_callbacks()) {}
+    Tree(size_t node_capacity, size_t arena_capacity, Callbacks const& cb);
+
+    ~Tree();
+
+    Tree(Tree const& that) noexcept;
+    Tree(Tree     && that) noexcept;
+
+    Tree& operator= (Tree const& that) noexcept;
+    Tree& operator= (Tree     && that) noexcept;
+
+    /** @} */
+
+public:
+
+    /** @name memory and sizing */
+    /** @{ */
+
+    void reserve(size_t node_capacity);
+
+    /** clear the tree and zero every node
+     * @note does NOT clear the arena
+     * @see clear_arena() */
+    void clear();
+    inline void clear_arena() { m_arena_pos = 0; }
+
+    inline bool   empty() const { return m_size == 0; }
+
+    inline size_t size() const { return m_size; }
+    inline size_t capacity() const { return m_cap; }
+    inline size_t slack() const { RYML_ASSERT(m_cap >= m_size); return m_cap - m_size; }
+
+    Callbacks const& callbacks() const { return m_callbacks; }
+    void callbacks(Callbacks const& cb) { m_callbacks = cb; }
+
+    /** @} */
+
+public:
+
+    /** @name node getters */
+    /** @{ */
+
+    //! get the index of a node belonging to this tree.
+    //! @p n can be nullptr, in which case a
+    size_t id(NodeData const* n) const
+    {
+        if( ! n)
+        {
+            return NONE;
+        }
+        RYML_ASSERT(n >= m_buf && n < m_buf + m_cap);
+        return static_cast<size_t>(n - m_buf);
+    }
+
+    //! get a pointer to a node's NodeData.
+    //! i can be NONE, in which case a nullptr is returned
+    inline NodeData *get(size_t i)
+    {
+        if(i == NONE)
+            return nullptr;
+        RYML_ASSERT(i >= 0 && i < m_cap);
+        return m_buf + i;
+    }
+    //! get a pointer to a node's NodeData.
+    //! i can be NONE, in which case a nullptr is returned.
+    inline NodeData const *get(size_t i) const
+    {
+        if(i == NONE)
+            return nullptr;
+        RYML_ASSERT(i >= 0 && i < m_cap);
+        return m_buf + i;
+    }
+
+    //! An if-less form of get() that demands a valid node index.
+    //! This function is implementation only; use at your own risk.
+    inline NodeData       * _p(size_t i)       { RYML_ASSERT(i != NONE && i >= 0 && i < m_cap); return m_buf + i; }
+    //! An if-less form of get() that demands a valid node index.
+    //! This function is implementation only; use at your own risk.
+    inline NodeData const * _p(size_t i) const { RYML_ASSERT(i != NONE && i >= 0 && i < m_cap); return m_buf + i; }
+
+    //! Get the id of the root node
+    size_t root_id()       { if(m_cap == 0) { reserve(16); } RYML_ASSERT(m_cap > 0 && m_size > 0); return 0; }
+    //! Get the id of the root node
+    size_t root_id() const {                                 RYML_ASSERT(m_cap > 0 && m_size > 0); return 0; }
+
+    //! Get a NodeRef of a node by id
+    NodeRef      ref(size_t id);
+    //! Get a NodeRef of a node by id
+    ConstNodeRef ref(size_t id) const;
+    //! Get a NodeRef of a node by id
+    ConstNodeRef cref(size_t id);
+    //! Get a NodeRef of a node by id
+    ConstNodeRef cref(size_t id) const;
+
+    //! Get the root as a NodeRef
+    NodeRef      rootref();
+    //! Get the root as a NodeRef
+    ConstNodeRef rootref() const;
+    //! Get the root as a NodeRef
+    ConstNodeRef crootref();
+    //! Get the root as a NodeRef
+    ConstNodeRef crootref() const;
+
+    //! find a root child by name, return it as a NodeRef
+    //! @note requires the root to be a map.
+    NodeRef      operator[] (csubstr key);
+    //! find a root child by name, return it as a NodeRef
+    //! @note requires the root to be a map.
+    ConstNodeRef operator[] (csubstr key) const;
+
+    //! find a root child by index: return the root node's @p i-th child as a NodeRef
+    //! @note @i is NOT the node id, but the child's position
+    NodeRef      operator[] (size_t i);
+    //! find a root child by index: return the root node's @p i-th child as a NodeRef
+    //! @note @i is NOT the node id, but the child's position
+    ConstNodeRef operator[] (size_t i) const;
+
+    //! get the i-th document of the stream
+    //! @note @i is NOT the node id, but the doc position within the stream
+    NodeRef      docref(size_t i);
+    //! get the i-th document of the stream
+    //! @note @i is NOT the node id, but the doc position within the stream
+    ConstNodeRef docref(size_t i) const;
+
+    /** @} */
+
+public:
+
+    /** @name node property getters */
+    /** @{ */
+
+    NodeType type(size_t node) const { return _p(node)->m_type; }
+    const char* type_str(size_t node) const { return NodeType::type_str(_p(node)->m_type); }
+
+    csubstr    const& key       (size_t node) const { RYML_ASSERT(has_key(node)); return _p(node)->m_key.scalar; }
+    csubstr    const& key_tag   (size_t node) const { RYML_ASSERT(has_key_tag(node)); return _p(node)->m_key.tag; }
+    csubstr    const& key_ref   (size_t node) const { RYML_ASSERT(is_key_ref(node) && ! has_key_anchor(node)); return _p(node)->m_key.anchor; }
+    csubstr    const& key_anchor(size_t node) const { RYML_ASSERT( ! is_key_ref(node) && has_key_anchor(node)); return _p(node)->m_key.anchor; }
+    NodeScalar const& keysc     (size_t node) const { RYML_ASSERT(has_key(node)); return _p(node)->m_key; }
+
+    csubstr    const& val       (size_t node) const { RYML_ASSERT(has_val(node)); return _p(node)->m_val.scalar; }
+    csubstr    const& val_tag   (size_t node) const { RYML_ASSERT(has_val_tag(node)); return _p(node)->m_val.tag; }
+    csubstr    const& val_ref   (size_t node) const { RYML_ASSERT(is_val_ref(node) && ! has_val_anchor(node)); return _p(node)->m_val.anchor; }
+    csubstr    const& val_anchor(size_t node) const { RYML_ASSERT( ! is_val_ref(node) && has_val_anchor(node)); return _p(node)->m_val.anchor; }
+    NodeScalar const& valsc     (size_t node) const { RYML_ASSERT(has_val(node)); return _p(node)->m_val; }
+
+    /** @} */
+
+public:
+
+    /** @name node predicates */
+    /** @{ */
+
+    C4_ALWAYS_INLINE bool is_stream(size_t node) const { return _p(node)->m_type.is_stream(); }
+    C4_ALWAYS_INLINE bool is_doc(size_t node) const { return _p(node)->m_type.is_doc(); }
+    C4_ALWAYS_INLINE bool is_container(size_t node) const { return _p(node)->m_type.is_container(); }
+    C4_ALWAYS_INLINE bool is_map(size_t node) const { return _p(node)->m_type.is_map(); }
+    C4_ALWAYS_INLINE bool is_seq(size_t node) const { return _p(node)->m_type.is_seq(); }
+    C4_ALWAYS_INLINE bool has_key(size_t node) const { return _p(node)->m_type.has_key(); }
+    C4_ALWAYS_INLINE bool has_val(size_t node) const { return _p(node)->m_type.has_val(); }
+    C4_ALWAYS_INLINE bool is_val(size_t node) const { return _p(node)->m_type.is_val(); }
+    C4_ALWAYS_INLINE bool is_keyval(size_t node) const { return _p(node)->m_type.is_keyval(); }
+    C4_ALWAYS_INLINE bool has_key_tag(size_t node) const { return _p(node)->m_type.has_key_tag(); }
+    C4_ALWAYS_INLINE bool has_val_tag(size_t node) const { return _p(node)->m_type.has_val_tag(); }
+    C4_ALWAYS_INLINE bool has_key_anchor(size_t node) const { return _p(node)->m_type.has_key_anchor(); }
+    C4_ALWAYS_INLINE bool is_key_anchor(size_t node) const { return _p(node)->m_type.is_key_anchor(); }
+    C4_ALWAYS_INLINE bool has_val_anchor(size_t node) const { return _p(node)->m_type.has_val_anchor(); }
+    C4_ALWAYS_INLINE bool is_val_anchor(size_t node) const { return _p(node)->m_type.is_val_anchor(); }
+    C4_ALWAYS_INLINE bool has_anchor(size_t node) const { return _p(node)->m_type.has_anchor(); }
+    C4_ALWAYS_INLINE bool is_anchor(size_t node) const { return _p(node)->m_type.is_anchor(); }
+    C4_ALWAYS_INLINE bool is_key_ref(size_t node) const { return _p(node)->m_type.is_key_ref(); }
+    C4_ALWAYS_INLINE bool is_val_ref(size_t node) const { return _p(node)->m_type.is_val_ref(); }
+    C4_ALWAYS_INLINE bool is_ref(size_t node) const { return _p(node)->m_type.is_ref(); }
+    C4_ALWAYS_INLINE bool is_anchor_or_ref(size_t node) const { return _p(node)->m_type.is_anchor_or_ref(); }
+    C4_ALWAYS_INLINE bool is_key_quoted(size_t node) const { return _p(node)->m_type.is_key_quoted(); }
+    C4_ALWAYS_INLINE bool is_val_quoted(size_t node) const { return _p(node)->m_type.is_val_quoted(); }
+    C4_ALWAYS_INLINE bool is_quoted(size_t node) const { return _p(node)->m_type.is_quoted(); }
+
+    C4_ALWAYS_INLINE bool parent_is_seq(size_t node) const { RYML_ASSERT(has_parent(node)); return is_seq(_p(node)->m_parent); }
+    C4_ALWAYS_INLINE bool parent_is_map(size_t node) const { RYML_ASSERT(has_parent(node)); return is_map(_p(node)->m_parent); }
+
+    /** true when key and val are empty, and has no children */
+    C4_ALWAYS_INLINE bool empty(size_t node) const { return ! has_children(node) && _p(node)->m_key.empty() && (( ! (_p(node)->m_type & VAL)) || _p(node)->m_val.empty()); }
+    /** true when the node has an anchor named a */
+    C4_ALWAYS_INLINE bool has_anchor(size_t node, csubstr a) const { return _p(node)->m_key.anchor == a || _p(node)->m_val.anchor == a; }
+
+    C4_ALWAYS_INLINE bool key_is_null(size_t node) const { RYML_ASSERT(has_key(node)); NodeData const* C4_RESTRICT n = _p(node); return !n->m_type.is_key_quoted() && _is_null(n->m_key.scalar); }
+    C4_ALWAYS_INLINE bool val_is_null(size_t node) const { RYML_ASSERT(has_val(node)); NodeData const* C4_RESTRICT n = _p(node); return !n->m_type.is_val_quoted() && _is_null(n->m_val.scalar); }
+    static bool _is_null(csubstr s) noexcept
+    {
+        return s.str == nullptr ||
+            s == "~" ||
+            s == "null" ||
+            s == "Null" ||
+            s == "NULL";
+    }
+
+    /** @} */
+
+public:
+
+    /** @name hierarchy predicates */
+    /** @{ */
+
+    bool is_root(size_t node) const { RYML_ASSERT(_p(node)->m_parent != NONE || node == 0); return _p(node)->m_parent == NONE; }
+
+    bool has_parent(size_t node) const { return _p(node)->m_parent != NONE; }
+
+    /** true if @p node has a child with id @p ch */
+    bool has_child(size_t node, size_t ch) const { return _p(ch)->m_parent == node; }
+    /** true if @p node has a child with key @p key */
+    bool has_child(size_t node, csubstr key) const { return find_child(node, key) != npos; }
+    /** true if @p node has any children key */
+    bool has_children(size_t node) const { return _p(node)->m_first_child != NONE; }
+
+    /** true if @p node has a sibling with id @p sib */
+    bool has_sibling(size_t node, size_t sib) const { return _p(node)->m_parent == _p(sib)->m_parent; }
+    /** true if one of the node's siblings has the given key */
+    bool has_sibling(size_t node, csubstr key) const { return find_sibling(node, key) != npos; }
+    /** true if node is not a single child */
+    bool has_other_siblings(size_t node) const
+    {
+        NodeData const *n = _p(node);
+        if(C4_LIKELY(n->m_parent != NONE))
+        {
+            n = _p(n->m_parent);
+            return n->m_first_child != n->m_last_child;
+        }
+        return false;
+    }
+
+    RYML_DEPRECATED("use has_other_siblings()") bool has_siblings(size_t /*node*/) const { return true; }
+
+    /** @} */
+
+public:
+
+    /** @name hierarchy getters */
+    /** @{ */
+
+    size_t parent(size_t node) const { return _p(node)->m_parent; }
+
+    size_t prev_sibling(size_t node) const { return _p(node)->m_prev_sibling; }
+    size_t next_sibling(size_t node) const { return _p(node)->m_next_sibling; }
+
+    /** O(#num_children) */
+    size_t num_children(size_t node) const;
+    size_t child_pos(size_t node, size_t ch) const;
+    size_t first_child(size_t node) const { return _p(node)->m_first_child; }
+    size_t last_child(size_t node) const { return _p(node)->m_last_child; }
+    size_t child(size_t node, size_t pos) const;
+    size_t find_child(size_t node, csubstr const& key) const;
+
+    /** O(#num_siblings) */
+    /** counts with this */
+    size_t num_siblings(size_t node) const { return is_root(node) ? 1 : num_children(_p(node)->m_parent); }
+    /** does not count with this */
+    size_t num_other_siblings(size_t node) const { size_t ns = num_siblings(node); RYML_ASSERT(ns > 0); return ns-1; }
+    size_t sibling_pos(size_t node, size_t sib) const { RYML_ASSERT( ! is_root(node) || node == root_id()); return child_pos(_p(node)->m_parent, sib); }
+    size_t first_sibling(size_t node) const { return is_root(node) ? node : _p(_p(node)->m_parent)->m_first_child; }
+    size_t last_sibling(size_t node) const { return is_root(node) ? node : _p(_p(node)->m_parent)->m_last_child; }
+    size_t sibling(size_t node, size_t pos) const { return child(_p(node)->m_parent, pos); }
+    size_t find_sibling(size_t node, csubstr const& key) const { return find_child(_p(node)->m_parent, key); }
+
+    size_t doc(size_t i) const { size_t rid = root_id(); RYML_ASSERT(is_stream(rid)); return child(rid, i); } //!< gets the @p i document node index. requires that the root node is a stream.
+
+    /** @} */
+
+public:
+
+    /** @name node modifiers */
+    /** @{ */
+
+    void to_keyval(size_t node, csubstr key, csubstr val, type_bits more_flags=0);
+    void to_map(size_t node, csubstr key, type_bits more_flags=0);
+    void to_seq(size_t node, csubstr key, type_bits more_flags=0);
+    void to_val(size_t node, csubstr val, type_bits more_flags=0);
+    void to_map(size_t node, type_bits more_flags=0);
+    void to_seq(size_t node, type_bits more_flags=0);
+    void to_doc(size_t node, type_bits more_flags=0);
+    void to_stream(size_t node, type_bits more_flags=0);
+
+    void set_key(size_t node, csubstr key) { RYML_ASSERT(has_key(node)); _p(node)->m_key.scalar = key; }
+    void set_val(size_t node, csubstr val) { RYML_ASSERT(has_val(node)); _p(node)->m_val.scalar = val; }
+
+    void set_key_tag(size_t node, csubstr tag) { RYML_ASSERT(has_key(node)); _p(node)->m_key.tag = tag; _add_flags(node, KEYTAG); }
+    void set_val_tag(size_t node, csubstr tag) { RYML_ASSERT(has_val(node) || is_container(node)); _p(node)->m_val.tag = tag; _add_flags(node, VALTAG); }
+
+    void set_key_anchor(size_t node, csubstr anchor) { RYML_ASSERT( ! is_key_ref(node)); _p(node)->m_key.anchor = anchor.triml('&'); _add_flags(node, KEYANCH); }
+    void set_val_anchor(size_t node, csubstr anchor) { RYML_ASSERT( ! is_val_ref(node)); _p(node)->m_val.anchor = anchor.triml('&'); _add_flags(node, VALANCH); }
+    void set_key_ref   (size_t node, csubstr ref   ) { RYML_ASSERT( ! has_key_anchor(node)); NodeData* C4_RESTRICT n = _p(node); n->m_key.set_ref_maybe_replacing_scalar(ref, n->m_type.has_key()); _add_flags(node, KEY|KEYREF); }
+    void set_val_ref   (size_t node, csubstr ref   ) { RYML_ASSERT( ! has_val_anchor(node)); NodeData* C4_RESTRICT n = _p(node); n->m_val.set_ref_maybe_replacing_scalar(ref, n->m_type.has_val()); _add_flags(node, VAL|VALREF); }
+
+    void rem_key_anchor(size_t node) { _p(node)->m_key.anchor.clear(); _rem_flags(node, KEYANCH); }
+    void rem_val_anchor(size_t node) { _p(node)->m_val.anchor.clear(); _rem_flags(node, VALANCH); }
+    void rem_key_ref   (size_t node) { _p(node)->m_key.anchor.clear(); _rem_flags(node, KEYREF); }
+    void rem_val_ref   (size_t node) { _p(node)->m_val.anchor.clear(); _rem_flags(node, VALREF); }
+    void rem_anchor_ref(size_t node) { _p(node)->m_key.anchor.clear(); _p(node)->m_val.anchor.clear(); _rem_flags(node, KEYANCH|VALANCH|KEYREF|VALREF); }
+
+    /** @} */
+
+public:
+
+    /** @name tree modifiers */
+    /** @{ */
+
+    /** reorder the tree in memory so that all the nodes are stored
+     * in a linear sequence when visited in depth-first order.
+     * This will invalidate existing ids, since the node id is its
+     * position in the node array. */
+    void reorder();
+
+    /** Resolve references (aliases <- anchors) in the tree.
+     *
+     * Dereferencing is opt-in; after parsing, Tree::resolve()
+     * has to be called explicitly for obtaining resolved references in the
+     * tree. This method will resolve all references and substitute the
+     * anchored values in place of the reference.
+     *
+     * This method first does a full traversal of the tree to gather all
+     * anchors and references in a separate collection, then it goes through
+     * that collection to locate the names, which it does by obeying the YAML
+     * standard diktat that "an alias node refers to the most recent node in
+     * the serialization having the specified anchor"
+     *
+     * So, depending on the number of anchor/alias nodes, this is a
+     * potentially expensive operation, with a best-case linear complexity
+     * (from the initial traversal). This potential cost is the reason for
+     * requiring an explicit call.
+     */
+    void resolve();
+
+    /** @} */
+
+public:
+
+    /** @name tag directives */
+    /** @{ */
+
+    void resolve_tags();
+
+    size_t num_tag_directives() const;
+    size_t add_tag_directive(TagDirective const& td);
+    void clear_tag_directives();
+
+    size_t resolve_tag(substr output, csubstr tag, size_t node_id) const;
+    csubstr resolve_tag_sub(substr output, csubstr tag, size_t node_id) const
+    {
+        size_t needed = resolve_tag(output, tag, node_id);
+        return needed <= output.len ? output.first(needed) : output;
+    }
+
+    using tag_directive_const_iterator = TagDirective const*;
+    tag_directive_const_iterator begin_tag_directives() const { return m_tag_directives; }
+    tag_directive_const_iterator end_tag_directives() const { return m_tag_directives + num_tag_directives(); }
+
+    struct TagDirectiveProxy
+    {
+        tag_directive_const_iterator b, e;
+        tag_directive_const_iterator begin() const { return b; }
+        tag_directive_const_iterator end() const { return e; }
+    };
+
+    TagDirectiveProxy tag_directives() const { return TagDirectiveProxy{begin_tag_directives(), end_tag_directives()}; }
+
+    /** @} */
+
+public:
+
+    /** @name modifying hierarchy */
+    /** @{ */
+
+    /** create and insert a new child of @p parent. insert after the (to-be)
+     * sibling @p after, which must be a child of @p parent. To insert as the
+     * first child, set after to NONE */
+    C4_ALWAYS_INLINE size_t insert_child(size_t parent, size_t after)
+    {
+        RYML_ASSERT(parent != NONE);
+        RYML_ASSERT(is_container(parent) || is_root(parent));
+        RYML_ASSERT(after == NONE || (_p(after)->m_parent == parent));
+        size_t child = _claim();
+        _set_hierarchy(child, parent, after);
+        return child;
+    }
+    /** create and insert a node as the first child of @p parent */
+    C4_ALWAYS_INLINE size_t prepend_child(size_t parent) { return insert_child(parent, NONE); }
+    /** create and insert a node as the last child of @p parent */
+    C4_ALWAYS_INLINE size_t  append_child(size_t parent) { return insert_child(parent, _p(parent)->m_last_child); }
+
+public:
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic push
+    #   pragma clang diagnostic ignored "-Wnull-dereference"
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic push
+    #   if __GNUC__ >= 6
+    #       pragma GCC diagnostic ignored "-Wnull-dereference"
+    #   endif
+    #endif
+
+    //! create and insert a new sibling of n. insert after "after"
+    C4_ALWAYS_INLINE size_t insert_sibling(size_t node, size_t after)
+    {
+        return insert_child(_p(node)->m_parent, after);
+    }
+    /** create and insert a node as the first node of @p parent */
+    C4_ALWAYS_INLINE size_t prepend_sibling(size_t node) { return prepend_child(_p(node)->m_parent); }
+    C4_ALWAYS_INLINE size_t  append_sibling(size_t node) { return append_child(_p(node)->m_parent); }
+
+public:
+
+    /** remove an entire branch at once: ie remove the children and the node itself */
+    inline void remove(size_t node)
+    {
+        remove_children(node);
+        _release(node);
+    }
+
+    /** remove all the node's children, but keep the node itself */
+    void remove_children(size_t node);
+
+    /** change the @p type of the node to one of MAP, SEQ or VAL.  @p
+     * type must have one and only one of MAP,SEQ,VAL; @p type may
+     * possibly have KEY, but if it does, then the @p node must also
+     * have KEY. Changing to the same type is a no-op. Otherwise,
+     * changing to a different type will initialize the node with an
+     * empty value of the desired type: changing to VAL will
+     * initialize with a null scalar (~), changing to MAP will
+     * initialize with an empty map ({}), and changing to SEQ will
+     * initialize with an empty seq ([]). */
+    bool change_type(size_t node, NodeType type);
+
+    bool change_type(size_t node, type_bits type)
+    {
+        return change_type(node, (NodeType)type);
+    }
+
+    #if defined(__clang__)
+    #   pragma clang diagnostic pop
+    #elif defined(__GNUC__)
+    #   pragma GCC diagnostic pop
+    #endif
+
+public:
+
+    /** change the node's position in the parent */
+    void move(size_t node, size_t after);
+
+    /** change the node's parent and position */
+    void move(size_t node, size_t new_parent, size_t after);
+
+    /** change the node's parent and position to a different tree
+     * @return the index of the new node in the destination tree */
+    size_t move(Tree * src, size_t node, size_t new_parent, size_t after);
+
+    /** ensure the first node is a stream. Eg, change this tree
+     *
+     *  DOCMAP
+     *    MAP
+     *      KEYVAL
+     *      KEYVAL
+     *    SEQ
+     *      VAL
+     *
+     * to
+     *
+     *  STREAM
+     *    DOCMAP
+     *      MAP
+     *        KEYVAL
+     *        KEYVAL
+     *      SEQ
+     *        VAL
+     *
+     * If the root is already a stream, this is a no-op.
+     */
+    void set_root_as_stream();
+
+public:
+
+    /** recursively duplicate a node from this tree into a new parent,
+     * placing it after one of its children
+     * @return the index of the copy */
+    size_t duplicate(size_t node, size_t new_parent, size_t after);
+    /** recursively duplicate a node from a different tree into a new parent,
+     * placing it after one of its children
+     * @return the index of the copy */
+    size_t duplicate(Tree const* src, size_t node, size_t new_parent, size_t after);
+
+    /** recursively duplicate the node's children (but not the node)
+     * @return the index of the last duplicated child */
+    size_t duplicate_children(size_t node, size_t parent, size_t after);
+    /** recursively duplicate the node's children (but not the node), where
+     * the node is from a different tree
+     * @return the index of the last duplicated child */
+    size_t duplicate_children(Tree const* src, size_t node, size_t parent, size_t after);
+
+    void duplicate_contents(size_t node, size_t where);
+    void duplicate_contents(Tree const* src, size_t node, size_t where);
+
+    /** duplicate the node's children (but not the node) in a new parent, but
+     * omit repetitions where a duplicated node has the same key (in maps) or
+     * value (in seqs). If one of the duplicated children has the same key
+     * (in maps) or value (in seqs) as one of the parent's children, the one
+     * that is placed closest to the end will prevail. */
+    size_t duplicate_children_no_rep(size_t node, size_t parent, size_t after);
+    size_t duplicate_children_no_rep(Tree const* src, size_t node, size_t parent, size_t after);
+
+public:
+
+    void merge_with(Tree const* src, size_t src_node=NONE, size_t dst_root=NONE);
+
+    /** @} */
+
+public:
+
+    /** @name internal string arena */
+    /** @{ */
+
+    /** get the current size of the tree's internal arena */
+    RYML_DEPRECATED("use arena_size() instead") size_t arena_pos() const { return m_arena_pos; }
+    /** get the current size of the tree's internal arena */
+    inline size_t arena_size() const { return m_arena_pos; }
+    /** get the current capacity of the tree's internal arena */
+    inline size_t arena_capacity() const { return m_arena.len; }
+    /** get the current slack of the tree's internal arena */
+    inline size_t arena_slack() const { RYML_ASSERT(m_arena.len >= m_arena_pos); return m_arena.len - m_arena_pos; }
+
+    /** get the current arena */
+    substr arena() const { return m_arena.first(m_arena_pos); }
+
+    /** return true if the given substring is part of the tree's string arena */
+    bool in_arena(csubstr s) const
+    {
+        return m_arena.is_super(s);
+    }
+
+    /** serialize the given floating-point variable to the tree's
+     * arena, growing it as needed to accomodate the serialization.
+     *
+     * @note Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual
+     * nodes, and thus cost O(numnodes)+O(arenasize). To avoid this
+     * cost, ensure that the arena is reserved to an appropriate size
+     * using .reserve_arena()
+     *
+     * @see alloc_arena() */
+    template<class T>
+    typename std::enable_if<std::is_floating_point<T>::value, csubstr>::type
+    to_arena(T const& C4_RESTRICT a)
+    {
+        substr rem(m_arena.sub(m_arena_pos));
+        size_t num = to_chars_float(rem, a);
+        if(num > rem.len)
+        {
+            rem = _grow_arena(num);
+            num = to_chars_float(rem, a);
+            RYML_ASSERT(num <= rem.len);
+        }
+        rem = _request_span(num);
+        return rem;
+    }
+
+    /** serialize the given non-floating-point variable to the tree's
+     * arena, growing it as needed to accomodate the serialization.
+     *
+     * @note Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual
+     * nodes, and thus cost O(numnodes)+O(arenasize). To avoid this
+     * cost, ensure that the arena is reserved to an appropriate size
+     * using .reserve_arena()
+     *
+     * @see alloc_arena() */
+    template<class T>
+    typename std::enable_if<!std::is_floating_point<T>::value, csubstr>::type
+    to_arena(T const& C4_RESTRICT a)
+    {
+        substr rem(m_arena.sub(m_arena_pos));
+        size_t num = to_chars(rem, a);
+        if(num > rem.len)
+        {
+            rem = _grow_arena(num);
+            num = to_chars(rem, a);
+            RYML_ASSERT(num <= rem.len);
+        }
+        rem = _request_span(num);
+        return rem;
+    }
+
+    /** serialize the given csubstr to the tree's arena, growing the
+     * arena as needed to accomodate the serialization.
+     *
+     * @note Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual
+     * nodes, and thus cost O(numnodes)+O(arenasize). To avoid this
+     * cost, ensure that the arena is reserved to an appropriate size
+     * using .reserve_arena()
+     *
+     * @see alloc_arena() */
+    csubstr to_arena(csubstr a)
+    {
+        if(a.len > 0)
+        {
+            substr rem(m_arena.sub(m_arena_pos));
+            size_t num = to_chars(rem, a);
+            if(num > rem.len)
+            {
+                rem = _grow_arena(num);
+                num = to_chars(rem, a);
+                RYML_ASSERT(num <= rem.len);
+            }
+            return _request_span(num);
+        }
+        else
+        {
+            if(a.str == nullptr)
+            {
+                return csubstr{};
+            }
+            else if(m_arena.str == nullptr)
+            {
+                // Arena is empty and we want to store a non-null
+                // zero-length string.
+                // Even though the string has zero length, we need
+                // some "memory" to store a non-nullptr string
+                _grow_arena(1);
+            }
+            return _request_span(0);
+        }
+    }
+    C4_ALWAYS_INLINE csubstr to_arena(const char *s)
+    {
+        return to_arena(to_csubstr(s));
+    }
+    C4_ALWAYS_INLINE csubstr to_arena(std::nullptr_t)
+    {
+        return csubstr{};
+    }
+
+    /** copy the given substr to the tree's arena, growing it by the
+     * required size
+     *
+     * @note Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual
+     * nodes, and thus cost O(numnodes)+O(arenasize). To avoid this
+     * cost, ensure that the arena is reserved to an appropriate size
+     * using .reserve_arena()
+     *
+     * @see alloc_arena() */
+    substr copy_to_arena(csubstr s)
+    {
+        substr cp = alloc_arena(s.len);
+        RYML_ASSERT(cp.len == s.len);
+        RYML_ASSERT(!s.overlaps(cp));
+        #if (!defined(__clang__)) && (defined(__GNUC__) && __GNUC__ >= 10)
+        C4_SUPPRESS_WARNING_GCC_PUSH
+        C4_SUPPRESS_WARNING_GCC("-Wstringop-overflow=") // no need for terminating \0
+        C4_SUPPRESS_WARNING_GCC( "-Wrestrict") // there's an assert to ensure no violation of restrict behavior
+        #endif
+        if(s.len)
+            memcpy(cp.str, s.str, s.len);
+        #if (!defined(__clang__)) && (defined(__GNUC__) && __GNUC__ >= 10)
+        C4_SUPPRESS_WARNING_GCC_POP
+        #endif
+        return cp;
+    }
+
+    /** grow the tree's string arena by the given size and return a substr
+     * of the added portion
+     *
+     * @note Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual
+     * nodes, and thus cost O(numnodes)+O(arenasize). To avoid this
+     * cost, ensure that the arena is reserved to an appropriate size
+     * using .reserve_arena().
+     *
+     * @see reserve_arena() */
+    substr alloc_arena(size_t sz)
+    {
+        if(sz > arena_slack())
+            _grow_arena(sz - arena_slack());
+        substr s = _request_span(sz);
+        return s;
+    }
+
+    /** ensure the tree's internal string arena is at least the given capacity
+     * @note This operation has a potential complexity of O(numNodes)+O(arenasize).
+     * Growing the arena may cause relocation of the entire
+     * existing arena, and thus change the contents of individual nodes. */
+    void reserve_arena(size_t arena_cap)
+    {
+        if(arena_cap > m_arena.len)
+        {
+            substr buf;
+            buf.str = (char*) m_callbacks.m_allocate(arena_cap, m_arena.str, m_callbacks.m_user_data);
+            buf.len = arena_cap;
+            if(m_arena.str)
+            {
+                RYML_ASSERT(m_arena.len >= 0);
+                _relocate(buf); // does a memcpy and changes nodes using the arena
+                m_callbacks.m_free(m_arena.str, m_arena.len, m_callbacks.m_user_data);
+            }
+            m_arena = buf;
+        }
+    }
+
+    /** @} */
+
+private:
+
+    substr _grow_arena(size_t more)
+    {
+        size_t cap = m_arena.len + more;
+        cap = cap < 2 * m_arena.len ? 2 * m_arena.len : cap;
+        cap = cap < 64 ? 64 : cap;
+        reserve_arena(cap);
+        return m_arena.sub(m_arena_pos);
+    }
+
+    substr _request_span(size_t sz)
+    {
+        substr s;
+        s = m_arena.sub(m_arena_pos, sz);
+        m_arena_pos += sz;
+        return s;
+    }
+
+    substr _relocated(csubstr s, substr next_arena) const
+    {
+        RYML_ASSERT(m_arena.is_super(s));
+        RYML_ASSERT(m_arena.sub(0, m_arena_pos).is_super(s));
+        auto pos = (s.str - m_arena.str);
+        substr r(next_arena.str + pos, s.len);
+        RYML_ASSERT(r.str - next_arena.str == pos);
+        RYML_ASSERT(next_arena.sub(0, m_arena_pos).is_super(r));
+        return r;
+    }
+
+public:
+
+    /** @name lookup */
+    /** @{ */
+
+    struct lookup_result
+    {
+        size_t  target;
+        size_t  closest;
+        size_t  path_pos;
+        csubstr path;
+
+        inline operator bool() const { return target != NONE; }
+
+        lookup_result() : target(NONE), closest(NONE), path_pos(0), path() {}
+        lookup_result(csubstr path_, size_t start) : target(NONE), closest(start), path_pos(0), path(path_) {}
+
+        /** get the part ot the input path that was resolved */
+        csubstr resolved() const;
+        /** get the part ot the input path that was unresolved */
+        csubstr unresolved() const;
+    };
+
+    /** for example foo.bar[0].baz */
+    lookup_result lookup_path(csubstr path, size_t start=NONE) const;
+
+    /** defaulted lookup: lookup @p path; if the lookup fails, recursively modify
+     * the tree so that the corresponding lookup_path() would return the
+     * default value.
+     * @see lookup_path() */
+    size_t lookup_path_or_modify(csubstr default_value, csubstr path, size_t start=NONE);
+
+    /** defaulted lookup: lookup @p path; if the lookup fails, recursively modify
+     * the tree so that the corresponding lookup_path() would return the
+     * branch @p src_node (from the tree @p src).
+     * @see lookup_path() */
+    size_t lookup_path_or_modify(Tree const *src, size_t src_node, csubstr path, size_t start=NONE);
+
+    /** @} */
+
+private:
+
+    struct _lookup_path_token
+    {
+        csubstr value;
+        NodeType type;
+        _lookup_path_token() : value(), type() {}
+        _lookup_path_token(csubstr v, NodeType t) : value(v), type(t) {}
+        inline operator bool() const { return type != NOTYPE; }
+        bool is_index() const { return value.begins_with('[') && value.ends_with(']'); }
+    };
+
+    size_t _lookup_path_or_create(csubstr path, size_t start);
+
+    void   _lookup_path       (lookup_result *r) const;
+    void   _lookup_path_modify(lookup_result *r);
+
+    size_t _next_node       (lookup_result *r, _lookup_path_token *parent) const;
+    size_t _next_node_modify(lookup_result *r, _lookup_path_token *parent);
+
+    void   _advance(lookup_result *r, size_t more) const;
+
+    _lookup_path_token _next_token(lookup_result *r, _lookup_path_token const& parent) const;
+
+private:
+
+    void _clear();
+    void _free();
+    void _copy(Tree const& that);
+    void _move(Tree      & that);
+
+    void _relocate(substr next_arena);
+
+public:
+
+    #if ! RYML_USE_ASSERT
+    C4_ALWAYS_INLINE void _check_next_flags(size_t, type_bits) {}
+    #else
+    void _check_next_flags(size_t node, type_bits f)
+    {
+        auto n = _p(node);
+        type_bits o = n->m_type; // old
+        C4_UNUSED(o);
+        if(f & MAP)
+        {
+            RYML_ASSERT_MSG((f & SEQ) == 0, "cannot mark simultaneously as map and seq");
+            RYML_ASSERT_MSG((f & VAL) == 0, "cannot mark simultaneously as map and val");
+            RYML_ASSERT_MSG((o & SEQ) == 0, "cannot turn a seq into a map; clear first");
+            RYML_ASSERT_MSG((o & VAL) == 0, "cannot turn a val into a map; clear first");
+        }
+        else if(f & SEQ)
+        {
+            RYML_ASSERT_MSG((f & MAP) == 0, "cannot mark simultaneously as seq and map");
+            RYML_ASSERT_MSG((f & VAL) == 0, "cannot mark simultaneously as seq and val");
+            RYML_ASSERT_MSG((o & MAP) == 0, "cannot turn a map into a seq; clear first");
+            RYML_ASSERT_MSG((o & VAL) == 0, "cannot turn a val into a seq; clear first");
+        }
+        if(f & KEY)
+        {
+            RYML_ASSERT(!is_root(node));
+            auto pid = parent(node); C4_UNUSED(pid);
+            RYML_ASSERT(is_map(pid));
+        }
+        if((f & VAL) && !is_root(node))
+        {
+            auto pid = parent(node); C4_UNUSED(pid);
+            RYML_ASSERT(is_map(pid) || is_seq(pid));
+        }
+    }
+    #endif
+
+    inline void _set_flags(size_t node, NodeType_e f) { _check_next_flags(node, f); _p(node)->m_type = f; }
+    inline void _set_flags(size_t node, type_bits  f) { _check_next_flags(node, f); _p(node)->m_type = f; }
+
+    inline void _add_flags(size_t node, NodeType_e f) { NodeData *d = _p(node); type_bits fb = f |  d->m_type; _check_next_flags(node, fb); d->m_type = (NodeType_e) fb; }
+    inline void _add_flags(size_t node, type_bits  f) { NodeData *d = _p(node);                f |= d->m_type; _check_next_flags(node,  f); d->m_type = f; }
+
+    inline void _rem_flags(size_t node, NodeType_e f) { NodeData *d = _p(node); type_bits fb = d->m_type & ~f; _check_next_flags(node, fb); d->m_type = (NodeType_e) fb; }
+    inline void _rem_flags(size_t node, type_bits  f) { NodeData *d = _p(node);            f = d->m_type & ~f; _check_next_flags(node,  f); d->m_type = f; }
+
+    void _set_key(size_t node, csubstr key, type_bits more_flags=0)
+    {
+        _p(node)->m_key.scalar = key;
+        _add_flags(node, KEY|more_flags);
+    }
+    void _set_key(size_t node, NodeScalar const& key, type_bits more_flags=0)
+    {
+        _p(node)->m_key = key;
+        _add_flags(node, KEY|more_flags);
+    }
+
+    void _set_val(size_t node, csubstr val, type_bits more_flags=0)
+    {
+        RYML_ASSERT(num_children(node) == 0);
+        RYML_ASSERT(!is_seq(node) && !is_map(node));
+        _p(node)->m_val.scalar = val;
+        _add_flags(node, VAL|more_flags);
+    }
+    void _set_val(size_t node, NodeScalar const& val, type_bits more_flags=0)
+    {
+        RYML_ASSERT(num_children(node) == 0);
+        RYML_ASSERT( ! is_container(node));
+        _p(node)->m_val = val;
+        _add_flags(node, VAL|more_flags);
+    }
+
+    void _set(size_t node, NodeInit const& i)
+    {
+        RYML_ASSERT(i._check());
+        NodeData *n = _p(node);
+        RYML_ASSERT(n->m_key.scalar.empty() || i.key.scalar.empty() || i.key.scalar == n->m_key.scalar);
+        _add_flags(node, i.type);
+        if(n->m_key.scalar.empty())
+        {
+            if( ! i.key.scalar.empty())
+            {
+                _set_key(node, i.key.scalar);
+            }
+        }
+        n->m_key.tag = i.key.tag;
+        n->m_val = i.val;
+    }
+
+    void _set_parent_as_container_if_needed(size_t in)
+    {
+        NodeData const* n = _p(in);
+        size_t ip = parent(in);
+        if(ip != NONE)
+        {
+            if( ! (is_seq(ip) || is_map(ip)))
+            {
+                if((in == first_child(ip)) && (in == last_child(ip)))
+                {
+                    if( ! n->m_key.empty() || has_key(in))
+                    {
+                        _add_flags(ip, MAP);
+                    }
+                    else
+                    {
+                        _add_flags(ip, SEQ);
+                    }
+                }
+            }
+        }
+    }
+
+    void _seq2map(size_t node)
+    {
+        RYML_ASSERT(is_seq(node));
+        for(size_t i = first_child(node); i != NONE; i = next_sibling(i))
+        {
+            NodeData *C4_RESTRICT ch = _p(i);
+            if(ch->m_type.is_keyval())
+                continue;
+            ch->m_type.add(KEY);
+            ch->m_key = ch->m_val;
+        }
+        auto *C4_RESTRICT n = _p(node);
+        n->m_type.rem(SEQ);
+        n->m_type.add(MAP);
+    }
+
+    size_t _do_reorder(size_t *node, size_t count);
+
+    void _swap(size_t n_, size_t m_);
+    void _swap_props(size_t n_, size_t m_);
+    void _swap_hierarchy(size_t n_, size_t m_);
+    void _copy_hierarchy(size_t dst_, size_t src_);
+
+    inline void _copy_props(size_t dst_, size_t src_)
+    {
+        _copy_props(dst_, this, src_);
+    }
+
+    inline void _copy_props_wo_key(size_t dst_, size_t src_)
+    {
+        _copy_props_wo_key(dst_, this, src_);
+    }
+
+    void _copy_props(size_t dst_, Tree const* that_tree, size_t src_)
+    {
+        auto      & C4_RESTRICT dst = *_p(dst_);
+        auto const& C4_RESTRICT src = *that_tree->_p(src_);
+        dst.m_type = src.m_type;
+        dst.m_key  = src.m_key;
+        dst.m_val  = src.m_val;
+    }
+
+    void _copy_props_wo_key(size_t dst_, Tree const* that_tree, size_t src_)
+    {
+        auto      & C4_RESTRICT dst = *_p(dst_);
+        auto const& C4_RESTRICT src = *that_tree->_p(src_);
+        dst.m_type = (src.m_type & ~_KEYMASK) | (dst.m_type & _KEYMASK);
+        dst.m_val  = src.m_val;
+    }
+
+    inline void _clear_type(size_t node)
+    {
+        _p(node)->m_type = NOTYPE;
+    }
+
+    inline void _clear(size_t node)
+    {
+        auto *C4_RESTRICT n = _p(node);
+        n->m_type = NOTYPE;
+        n->m_key.clear();
+        n->m_val.clear();
+        n->m_parent = NONE;
+        n->m_first_child = NONE;
+        n->m_last_child = NONE;
+    }
+
+    inline void _clear_key(size_t node)
+    {
+        _p(node)->m_key.clear();
+        _rem_flags(node, KEY);
+    }
+
+    inline void _clear_val(size_t node)
+    {
+        _p(node)->m_val.clear();
+        _rem_flags(node, VAL);
+    }
+
+private:
+
+    void _clear_range(size_t first, size_t num);
+
+    size_t _claim();
+    void   _claim_root();
+    void   _release(size_t node);
+    void   _free_list_add(size_t node);
+    void   _free_list_rem(size_t node);
+
+    void _set_hierarchy(size_t node, size_t parent, size_t after_sibling);
+    void _rem_hierarchy(size_t node);
+
+public:
+
+    // members are exposed, but you should NOT access them directly
+
+    NodeData * m_buf;
+    size_t m_cap;
+
+    size_t m_size;
+
+    size_t m_free_head;
+    size_t m_free_tail;
+
+    substr m_arena;
+    size_t m_arena_pos;
+
+    Callbacks m_callbacks;
+
+    TagDirective m_tag_directives[RYML_MAX_TAG_DIRECTIVES];
+
+};
+
+} // namespace yml
+} // namespace c4
+
+
+C4_SUPPRESS_WARNING_MSVC_POP
+C4_SUPPRESS_WARNING_GCC_CLANG_POP
+
+
+#endif /* _C4_YML_TREE_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/writer.hpp b/thirdparty/ryml/src/c4/yml/writer.hpp
new file mode 100644
index 000000000..29e32d47b
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/writer.hpp
@@ -0,0 +1,229 @@
+#ifndef _C4_YML_WRITER_HPP_
+#define _C4_YML_WRITER_HPP_
+
+#ifndef _C4_YML_COMMON_HPP_
+#include "./common.hpp"
+#endif
+
+#include <c4/substr.hpp>
+#include <stdio.h>  // fwrite(), fputc()
+#include <string.h> // memcpy()
+
+
+namespace c4 {
+namespace yml {
+
+
+/** Repeat-Character: a character to be written a number of times. */
+struct RepC
+{
+    char c;
+    size_t num_times;
+};
+inline RepC indent_to(size_t num_levels)
+{
+    return {' ', size_t(2) * num_levels};
+}
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+/** A writer that outputs to a file. Defaults to stdout. */
+struct WriterFile
+{
+    FILE * m_file;
+    size_t m_pos;
+
+    WriterFile(FILE *f = nullptr) : m_file(f ? f : stdout), m_pos(0) {}
+
+    inline substr _get(bool /*error_on_excess*/)
+    {
+        substr sp;
+        sp.str = nullptr;
+        sp.len = m_pos;
+        return sp;
+    }
+
+    template<size_t N>
+    inline void _do_write(const char (&a)[N])
+    {
+        fwrite(a, sizeof(char), N - 1, m_file);
+        m_pos += N - 1;
+    }
+
+    inline void _do_write(csubstr sp)
+    {
+        #if defined(__clang__)
+        #   pragma clang diagnostic push
+        #   pragma GCC diagnostic ignored "-Wsign-conversion"
+        #elif defined(__GNUC__)
+        #   pragma GCC diagnostic push
+        #   pragma GCC diagnostic ignored "-Wsign-conversion"
+        #endif
+        if(sp.empty()) return;
+        fwrite(sp.str, sizeof(csubstr::char_type), sp.len, m_file);
+        m_pos += sp.len;
+        #if defined(__clang__)
+        #   pragma clang diagnostic pop
+        #elif defined(__GNUC__)
+        #   pragma GCC diagnostic pop
+        #endif
+    }
+
+    inline void _do_write(const char c)
+    {
+        fputc(c, m_file);
+        ++m_pos;
+    }
+
+    inline void _do_write(RepC const rc)
+    {
+        for(size_t i = 0; i < rc.num_times; ++i)
+        {
+            fputc(rc.c, m_file);
+        }
+        m_pos += rc.num_times;
+    }
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+/** A writer that outputs to an STL-like ostream. */
+template<class OStream>
+struct WriterOStream
+{
+    OStream& m_stream;
+    size_t   m_pos;
+
+    WriterOStream(OStream &s) : m_stream(s), m_pos(0) {}
+
+    inline substr _get(bool /*error_on_excess*/)
+    {
+        substr sp;
+        sp.str = nullptr;
+        sp.len = m_pos;
+        return sp;
+    }
+
+    template<size_t N>
+    inline void _do_write(const char (&a)[N])
+    {
+        m_stream.write(a, N - 1);
+        m_pos += N - 1;
+    }
+
+    inline void _do_write(csubstr sp)
+    {
+        #if defined(__clang__)
+        #   pragma clang diagnostic push
+        #   pragma GCC diagnostic ignored "-Wsign-conversion"
+        #elif defined(__GNUC__)
+        #   pragma GCC diagnostic push
+        #   pragma GCC diagnostic ignored "-Wsign-conversion"
+        #endif
+        if(sp.empty()) return;
+        m_stream.write(sp.str, sp.len);
+        m_pos += sp.len;
+        #if defined(__clang__)
+        #   pragma clang diagnostic pop
+        #elif defined(__GNUC__)
+        #   pragma GCC diagnostic pop
+        #endif
+    }
+
+    inline void _do_write(const char c)
+    {
+        m_stream.put(c);
+        ++m_pos;
+    }
+
+    inline void _do_write(RepC const rc)
+    {
+        for(size_t i = 0; i < rc.num_times; ++i)
+        {
+            m_stream.put(rc.c);
+        }
+        m_pos += rc.num_times;
+    }
+};
+
+
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+/** a writer to a substr */
+struct WriterBuf
+{
+    substr m_buf;
+    size_t m_pos;
+
+    WriterBuf(substr sp) : m_buf(sp), m_pos(0) {}
+
+    inline substr _get(bool error_on_excess)
+    {
+        if(m_pos <= m_buf.len)
+        {
+            return m_buf.first(m_pos);
+        }
+        if(error_on_excess)
+        {
+            c4::yml::error("not enough space in the given buffer");
+        }
+        substr sp;
+        sp.str = nullptr;
+        sp.len = m_pos;
+        return sp;
+    }
+
+    template<size_t N>
+    inline void _do_write(const char (&a)[N])
+    {
+        RYML_ASSERT( ! m_buf.overlaps(a));
+        if(m_pos + N-1 <= m_buf.len)
+        {
+            memcpy(&(m_buf[m_pos]), a, N-1);
+        }
+        m_pos += N-1;
+    }
+
+    inline void _do_write(csubstr sp)
+    {
+        if(sp.empty()) return;
+        RYML_ASSERT( ! sp.overlaps(m_buf));
+        if(m_pos + sp.len <= m_buf.len)
+        {
+            memcpy(&(m_buf[m_pos]), sp.str, sp.len);
+        }
+        m_pos += sp.len;
+    }
+
+    inline void _do_write(const char c)
+    {
+        if(m_pos + 1 <= m_buf.len)
+        {
+            m_buf[m_pos] = c;
+        }
+        ++m_pos;
+    }
+
+    inline void _do_write(RepC const rc)
+    {
+        if(m_pos + rc.num_times <= m_buf.len)
+        {
+            for(size_t i = 0; i < rc.num_times; ++i)
+            {
+                m_buf[m_pos + i] = rc.c;
+            }
+        }
+        m_pos += rc.num_times;
+    }
+};
+
+
+} // namespace yml
+} // namespace c4
+
+#endif /* _C4_YML_WRITER_HPP_ */
diff --git a/thirdparty/ryml/src/c4/yml/yml.hpp b/thirdparty/ryml/src/c4/yml/yml.hpp
new file mode 100644
index 000000000..36f78fe82
--- /dev/null
+++ b/thirdparty/ryml/src/c4/yml/yml.hpp
@@ -0,0 +1,10 @@
+#ifndef _C4_YML_YML_HPP_
+#define _C4_YML_YML_HPP_
+
+#include "c4/yml/tree.hpp"
+#include "c4/yml/node.hpp"
+#include "c4/yml/emit.hpp"
+#include "c4/yml/parse.hpp"
+#include "c4/yml/preprocess.hpp"
+
+#endif // _C4_YML_YML_HPP_