The return values of lua_load are:

automatically detects whether the chunk is text or binary, and loads it accordingly (see program luac).

In the current implementation, the reader function cannot call any Lua function; to ensure that, it always receives NULL as the Lua state.

See the auxiliary library (lauxlib.c) for examples of how to use lua_load and for some ready-to-use functions to load chunks from files and strings.