         
         /**
          *  @private
-         *  True while updateDisplayList is running.
-         */
-        private var inUpdateDisplayList:Boolean = false;
+         *  True while updateDisplayList is running.  Use to disable invalidateSize(),
+         *  invalidateDisplayList() here and in the GridLayer class.
+         */
+        mx_internal var inUpdateDisplayList:Boolean = false;  
         
         
         // TODO(hmuller): the following public variables are temporary 

        }
    }
}

import spark.layouts.supportClasses.LayoutBase;

class NullLayout extends LayoutBase
{
    public function NullLayout()
    {
        super();
    }
}
            super();
            layout = new GridLayout();
            
            backgroundGroup = new GridLayer();
            addElement(backgroundGroup);
            
            selectionGroup = new GridLayer();
            addElement(selectionGroup);
            
            itemRendererGroup = this;
            
            overlayGroup = new GridLayer();
            addElement(overlayGroup);        
            
            MouseEventUtil.addDownDragUpListeners(this, 
