There is a different between background scripts, and “one-shot” scripts (those that you run from an action, the menu, etc.).
The “begin/end.” block (with the period, at the end of the script), is the “main program” in a script. This is what is being executed when you run a “one-shot” script.
Background scripts don’t need a main program, because they are basically a collection of procedures that are executed individually by the mAirList script engine.
That being said, even the background scripts do require an (empty) main program in order to compile correctly (make them a valid script). But mAirList will add it for you automatically. So no need to type it manually.