             }
             if (!isNaN(vspDelta))
             {
-            	viewport.verticalScrollPosition += vspDelta;
+            	vp.verticalScrollPosition += vspDelta;
             	event.stopPropagation();
             }
         }

     */
    override protected function keyDownHandler(event:KeyboardEvent):void
    {
    	if (!viewport)
    	    return;
    	    
        // TBD: is special handling for textfields needed here, as in mx.core.Container?
    
        // TBD: IViewport should expose horiztonal,verticalScrollPositionDelta methods
        var vp:LayoutBase = LayoutBase(Group(viewport).layout);
         
        if (verticalScrollBar && verticalScrollBar.visible)
        {
        	var vspDelta:Number = NaN;

            }
            if (!isNaN(hspDelta))
            {
                vp.horizontalScrollPosition += hspDelta;
                event.stopPropagation();
            }
        }
