AS2 was an anarchy language, if you need to put a movieClip visually above all the things in the stage, you can do movieClip.swapDepths(this.getNextHighestDepth()). So it works, but in reality your are swapping your movieClip with a movieClip that didn’t exist, so in AS3 you can’t do that but we have setChildIndex method. You Can do setChildIndex(numChildren-1)
AS2
AS3