I, Luke T. Shumaker, am the sole author of the added code. I did not reference CVTUTF when writing it. I did reference the Unicode standard (15.0.0), the Wikipedia article on UTF-8, and the Wikipedia article on UTF-16. When I saw some tests fail, I did reference the old deleted code (but a JSON-specific part, inherently not as based on CVTUTF) to determine that script_safe should also escape U+2028 and U+2029. I targeted simplicity and clarity when writing the code--it can likely be optimized. In my mind, the obvious next optimization is to have it combine contiguous non-escaped characters into just one call to fbuffer_append(), instead of calling fbuffer_append() for each character. Regarding the use of the "modern" types `uint32_t`, `uint16_t`, and `bool`: - ruby.h is guaranteed to give us uint32_t and uint16_t. - Since Ruby 3.0.0, ruby.h is guaranteed to give us bool... but we support down to Ruby 2.3. But, ruby.h is guaranteed to give us HAVE_STDBOOL_H for the C99 stdbool.h; so use that to include stdbool.h if we can, and if not then fall back to a copy of the same bool definition that Ruby 3.0.5 uses with C89. https://github.com/ruby/json/commit/c96351f874