 import mx.core.IFactory;
 import mx.core.IViewport;
 import mx.core.IVisualElement;
-import mx.core.ScrollUnit;
 import mx.core.UIComponent;
 import mx.core.mx_internal;
 import mx.events.CollectionEvent;
 import mx.events.FlexEvent;
-import mx.events.ItemExistenceChangedEvent;
+import mx.events.RendererExistenceEvent;
 import mx.events.PropertyChangeEvent;
 import mx.events.PropertyChangeEventKind;
 import mx.graphics.Graphic;

    }
    
    //----------------------------------
    //  clipContent
    //----------------------------------
    
    /**
     *  @copy mx.core.IViewport#clipContent
     */
    public function get clipContent():Boolean 
    {
        return (_layout) ? _layout.clipContent : _layoutProperties.clipContent;
    }

    /**
     *  @private
     */
    public function set clipContent(value:Boolean):void 
    {
        if (_layout)
            _layout.clipContent = value;
        else
            _layoutProperties.clipContent = value;

        // Clip content affects measured minimum size
        invalidateSize();
    }    
    

    /**
     *  @private
     * 
     *  Three properties are delegated to the layout: clipAndEnableScrolling,
     *  verticalScrollPosition, horizontalScrollPosition.
     *  If the layout is reset, we copy the properties from the old
     *  layout to the new one.   If the new layout is null, then we
