      * 
      *  @see ScrollUnit
      */
-    function getVerticalScrollPositionDelta(unit:ScrollUnit):Number;
+    function getVerticalScrollPositionDelta(scrollUnit:uint):Number;
      
     /**
-     *  If true then clip the viewport's contents by setting its scrollRect
+     *  This flag must set to true to enable scrolling via the
+     *  vertical and horizontalScrollPosition properties. 
+     *  
+     *  If true then viewport's contents are clipped by setting its scrollRect
      *  to a rectangle with origin at horizontalScrollPosition,
      *  verticalScrollPosition and width and height equal to the 
      *  viewport's width and height.

     *  @see verticalScrollPosition
     *  @see horizontalScrollPosition
     */
    function get clipContent():Boolean;
    function set clipContent(value:Boolean):void;    
}

}

     *  The X coordinate of the origin of the region the target is
     *  scrolled to.  
     * 
     *  If clipAndEnableScrolling is true, setting this property typically causes 
     *  <code>scrollRect</code> to be set to:
     *  <pre>
     *  new Rectangle(horizontalScrollPosition, verticalScrollPosition, width, height)
