Flash MX 2004.
document.library
Read-only property; the library object for a document.
The following example gets the library for the currently focused document:
var myCurrentLib = fl.getDocumentDOM().library;
Assuming the currently focused document is not fl.documents[1], the following example gets the library for a nonfocused library or for a library you opened using File >Open as external library:
var externalLib = fl.documents[1].library;