g_BIF is an array of FuncEntry that stores al built-in functions. g_BIV is an array of VarEntry that stores the built-in variables whose name don't start with A_. g_BIV_A is also an array of VarEntry that stores the built-in variables whose name start with A_. Script::Init(…) seems to be called with the filename of the script that was passed when AutoHotKey was started.