[LUA 5.1] setfenv

Sets the environment to be used by the given function.
f can be a Lua function or a number that specifies the function at that stack level: Level 1 is the function calling setfenv.
setfenv returns the given function.

As a special case, when f is 0 setfenv changes the environment of the running thread.
In this case, setfenv returns no values.