table? - table to check the the key in; if omitted, defaults to the globals table (_G).
string - string key to check the taint of. Numbers will be converted to a string; other types will throw an error.
boolean - true if the table[variable] key is secure, false if it is tainted.
string? - name of the addon that tainted the table field; an empty string if tainted by a macro; nil if secure.
Also returns true, nil for keys that have never been used/defined, because nothing has tainted them yet.
If table[variable] == nil, and table has a metatable with __index, this function will return whether the metatable's __index[varible] is tainted. You must remove the metatable to check whether table[variable] itself is tainted.
Cannot be used to check taint of local variables, or non-string table keys.