ActionScript for Flash MX: The Definitive Guide, 2nd Edition By Colin Moock
Chapter 10. Events and Event Handling
The lifespan of event handlers is tied to the life of the objects with which they are associated. When a clip or button is removed from the Stage, or when an XML or TextField object is deleted, any event handlers associated with those objects die with them. An object must be present on stage or in code for its handlers to remain active.
