flash mask

    var panel:Panel = new Panel();
    panel.title = "Mask";
    panel.width = 400;
    panel.height = 300;
    panel.x = -200;
    panel.y = 50;
    bc.addElement(panel);
    
    var s:Shape = new Shape();
    s.graphics.clear();
    s.graphics.beginFill(0, 1);
    s.graphics.drawRect(0, 0, 100, 32);
    s.graphics.endFill();
    
    var pos:Point = panel.parent.localToGlobal(new Point(panel.x, panel.y));
    s.x = pos.x;
    s.y = pos.y;
    
    panel.mask = s;