             measureReal(layoutTarget);
     }
     
-    //  - virtual layout only - 
+    /**
+     *  @private
+     * 
+     *  Used only for virtual layout.
+     */
     private function calculateElementHeight(elt:ILayoutElement, targetHeight:Number, containerHeight:Number):Number
     {
        // If percentHeight is specified then the element's height is the percentage

    }

    /**
     *  If the element at index i is non-null and includeInLayout,
     *  then return it's actual bounds, otherwise return null.
     * 
     *  @private
     */
    private function layoutElementBounds(g:GroupBase, i:int):Rectangle
    {

    }

    /**
     *  @private
     * 
     *  Sets the <code>columnCount</code> property and dispatches
     *  a PropertyChangeEvent.
     */
    private function setColumnCount(value:int):void
    {
        if (_columnCount == value)
            return;
