Sheesh...I just wasted half a day trying to figure out how to get a borderSkin to appear on top of all the children in a custom component I was building. It was a subclass of Canvas, so it was really easy...now that I know, it seems so obvious I want to kick myself. Anyway, you just need to do:

PLAIN TEXT
Actionscript:
  1. override protected function layoutChrome(unscaledWidth:Number,unscaledHeight:Number):void{
  2.     super.layoutChrome(unscaledWidth, unscaledHeight);
  3.    
  4.     //move the border in front of the children
  5.     rawChildren.setChildIndex(rawChildren.getChildByName('border'), rawChildren.numChildren - 1);         
  6.  
  7. }