     }
     
     /**
-     *  @inheritDoc
-     */
+     *  Returns the 0 if the item passed in is the viewport.  
+     *  Otherwise, it throws an ArgumentError.
+     *
+     *  @param item The item to identify.
+     *
+     *  @return The index position of the item to identify.
+     * 
+     *  @throws ArgumentError If the item is not a child of this object.
+     */ 
     public function getItemIndex(item:Object):int
     {
         if (item != null && item == viewport)

    }
    
    /**
     *  @inheritDoc
     */
    public function getItemAt(index:int):Object
    {
        if (viewport && index == 0)

    //--------------------------------------------------------------------------

    /**
     *  Returns 1 if there is a viewport, 0 otherwise.
     */
    public function get numItems():int
    {
