Flex NativeDrag Event on an mx:Html control?

Question

I have an mx:HTML tag loading external content. The control takes up 100%w and 100%height of the application.

How can I accept NativeDrag (or any drag) events and receive the drops?

    <mx:Canvas width="100%" height="100%" backgroundColor="#000000" id="cvDropZone">
 <mx:HTML id="coreHtml" width="100%" height="100%" backgroundColor="red" dragDrop="onDrop(event)">

 </mx:HTML>
</mx:Canvas>

private function onDrop(e:DragEvent):void{    
   trace("onDrop: " + e.target.toString());    
  }

onDrop never gets called?