Code on objects, including on() and onClipEvent(), are no longer supported in ActionScript 3.0. The Flash 9 preview still allows you to put code in there, but if you compile you’ll get the following error:
WARNING: ActionScript 3.0 does not support actions on button or MovieClip instances. All scripts on object instances will be ignored.
This is great news for all of us Flash Developers that are sick and tired of hunting through FLA files to find code buried on objects. :)
All events in AS3 will be running through the new and improved Event Framework built-in to Flash Player 9. This allows for consistent event implementation across all built-in and custom objects, since there is now only one event system.