In as3, the introduction to of the display list has made the
stop() method a little less straightforward. Traditionally, when you used
stop() on the timeline of a movieclip, it would do just that, stop the playhead from playing past where that script is. To be fare, this does still work, but only if you place the movieclip on the timeline manually (not via code).
Now to get a movieclip to stop on the first frame when added to the display list via the
addChild() method, you must be sure to add
stop() once it’s added. Also, note that you cannot call any other timeline based methods such as
gotoAndStop() to a dynamically added movieclip unless it’s on the display list either.
This is specifically useful when you are using a movieclip that has a timeline based rollover and rollout animation as a button.