Flash CS3 Professional.
document.docClass
Property; a string that specifies the top-level ActionScript 3.0 class associated with the document. If the document isn’t configured to use ActionScript 3.0, this property is ignored.
The following example specifies that the ActionScript 3.0 class associated with the document is com.mycompany.ManagerClass, which is defined in com/mycompany/ManagerClass.as:
var myDocument = fl.getDocumentDOM();
// set the property
myDocument.docClass = "com.mycompany.ManagerClass";
// get the property
fl.outputPanel.trace("document.docClass has been set to " + myDocument.docClass);