user data

[Philipp Kraus <philipp.kraus@...>]

Hello,

I have found in the C reference of Lua the functions
lua_islightuserdata
lua_isuserdata

What is the "user data" ? Eg I have got a Lua function that returns something, which datatype should I return, so one of these function will be true.
How can I handle "user data" in C ?

Thanks

Phil