Masking out off-stage content of loaded .swf?

I’m just starting out with AS3 and this is what I’m trying to do:

  1. I have an external .swf banner which is 900x250 pixels
  2. I want to load this .swf into my main project, using this code:

var myLoader:Loader = new Loader();
var myRequest:URLRequest = new URLRequest(“ptp.swf”);

  1. The problem is that the .swf banner that is being loaded has content ‘outside the stage’ so instead of just showing the 900x250 area I see all the off-stage content as well.

How do I ‘mask out’ the off-stage content of the loaded .swf so that it will be only the 900x250 that I want?

Thanks in advance!!