     /**
      *  @copy flex.intf.IViewport#verticalScrollPositionDelta
      */
-    public function verticalScrollPositionDelta(unit:uint):Number
+    public function getVerticalScrollPositionDelta(unit:ScrollUnit):Number
     {
         var g:GroupBase = target;
         if (!g)

    }
    
    /**
     *  Conditionally sets the origin of the scrollRect to 
     *  verticalScrollPosition,horizontalScrollPosition and its width
     *  width,height to w,h (the target's unscaled width,height).
     * 
     *  This method must be called by updateDisplayList after the 
     *  target's contentWidth and contentHeight properties have been 
     *  set to the display list's actual limits.
     * 
     *  The target's scrollRect property is set if its contentWidth,Height
     *  is larger than its width,height, or the target's 
     *  vertical,horizontalScrollPosition is non-zero.
     * 
     *  If none of the above conditions are true, or if clipContent
     *  is false, then the scrollRect is set to null.
     * 
     *  @param w The target's unscaled width.
     *  @param h The target's unscaled height.
     * 
     *  @see target
     *  @see flash.display.DisplayObject#scrollRect
     *  @see updateDisplayList
     *  @see mx.components.GroupBase#contentWidth
     *  @see mx.components.GroupBase#contentHeight
     */ 
    protected function updateScrollRect(w:Number, h:Number):void
    {
        var g:GroupBase = target;
        if (!g)
            return;
            
        if (!clipContent)
        {
            g.scrollRect = null;
            return;
        }            

        var hsp:Number = horizontalScrollPosition;
        var vsp:Number = verticalScrollPosition;
        var cw:Number = g.contentWidth;
        var ch:Number = g.contentHeight;
            
        // Don't set the scrollRect needlessly.
        if ((hsp != 0) || (vsp != 0) || (cw > w) || (ch > h))
            g.scrollRect = new Rectangle(hsp, vsp, w, h);
        else 
            g.scrollRect = null;
    } 
    

            
        switch (unit)
        {
            case ScrollUnit.LEFT:
                return (scrollR.x <= 0) ? 0 : -1;
                
            case ScrollUnit.RIGHT:
                return (scrollR.x >= maxDelta) ? 0 : 1;
                
            case ScrollUnit.PAGE_LEFT:
                return Math.max(minDelta, -scrollR.width);
                
            case ScrollUnit.PAGE_RIGHT:
                return Math.min(maxDelta, scrollR.width);
                
            case ScrollUnit.HOME: 
                return minDelta;
                
            case ScrollUnit.END: 
                return maxDelta;
                
            default:
