     
     /**
      *  @private
-     *  Called after super.updateDisplayList() finishes.
+     *  Called after super.updateDisplayList() finishes.  Also called by
+     *  createItemRenderers to recycle existing renderers that were added
+     *  to oldVirtualRendererIndices by the preceeding call to 
+     *  startVirtualLayout.
      * 
      *  Discard the ItemRenderers that aren't needed anymore, i.e. the ones
      *  not explicitly requested with getVirtualElementAt() during the most

            removeAllItemRenderers();   // indexToRenderer.length = 0

        if (layout && layout.useVirtualLayout)
        {
            // The item renderers will be created lazily, at updateDisplayList() time
            invalidateSize();
            invalidateDisplayList();

    /**
     *  @private
     *  Called before super.updateDisplayList() if layout.useVirtualLayout=true.
     *  Also called by createItemRenderers to ready existing renderers
     *  to be recycled by the following call to finishVirtualLayout.
     * 
     *  Copies virtualRendererIndices to oldRendererIndices, clears virtualRendererIndices
     *  (which will be repopulated by subsequence getVirtualElementAt() calls), and
     *  calls ensureTypicalElement().
