This is a patched PUC-Lua exposing low-level implementation details. This version of Lua is used by some experimental projects including Pallene and LuaAOT.
Use these internal APIs at your own risk! They are unstable and may change even after a bugfix patch (e.g. 5.4.2 -> 5.4.3). Additionally, they are unsafe. You can easily get a segfault or worse if you don't know what you are doing.
Compile and install using the provided Makefile, the same way you would for upstream PUC-Lua. Detailed instructions can be found in the doc/readme.html.
There is a new header file called luacore.h,
which contains all the internals APIs from the Lua core (e.g lgc.h, lstring.h, etc).
There is a new function luaL_checkcoreversion in lauxlib.h.
It is similar to luaL_checkversion, except that also compares the patch number (e.g. 5.4.2 vs 5.4.3).