Creating Libraries
From QuestWiki
Libraries have the same format as a game ASLX file, except that the parent attribute is <library>.
Because libraries are otherwise ordinary ASLX files, they can define objects, functions, types, and everything else that an ordinary game file can define.
If you create a library, it is a good idea to add Editor elements to it, so that users of your library can easily use its features. For information, please see Editor User Interface Elements.
See also Using libraries