    /**
     * DD implementation for Panels.
     * @private
     */
    Ext.define('Ext.panel.DD', {
        extend: 'Ext.dd.DragSource',
        requires: ['Ext.panel.Proxy'],

        constructor : function(panel, cfg){
            var me = this;

            me.panel = panel;
            me.dragData = {panel: panel};
            me.panelProxy = new Ext.panel.Proxy(panel, cfg);
            me.proxy = me.panelProxy.proxy;

            me.callParent([panel.el, cfg]);
            me.setupEl(panel);
        },

        setupEl: function(panel){
            var me = this,
                header = panel.header,
                el = panel.body;

            if (header) {
                me.setHandleElId(header.id);
                el = header.el;
            }
            if (el) {
                el.setStyle('cursor', 'move');
                me.scroll = false;
            } else {
                // boxready fires after first layout, so we'll definitely be rendered
                panel.on('boxready', me.setupEl, me, {single: true});
            }
        },

        showFrame: Ext.emptyFn,
        startDrag: Ext.emptyFn,

        b4StartDrag: function(x, y) {
            this.panelProxy.show();
        },

        b4MouseDown: function(e) {
            var x = e.getPageX(),
                y = e.getPageY();

            this.autoOffset(x, y);
        },

        onInitDrag : function(x, y){
            this.onStartDrag(x, y);
            return true;
        },

        createFrame : Ext.emptyFn,

        getDragEl : function(e){
            return this.panelProxy.ghost.el.dom;
        },

        endDrag : function(e){
            this.panelProxy.hide();
            this.panel.saveState();
        },

        autoOffset : function(x, y) {
            x -= this.startPageX;
            y -= this.startPageY;
            this.setDelta(x, y);
        },

        // Override this, we don't want to repair on an "invalid" drop, the panel
        // should main it's position
        onInvalidDrop: function(target, e, id) {
            var me = this;

            me.beforeInvalidDrop(target, e, id);
            if (me.cachedTarget) {
                if(me.cachedTarget.isNotifyTarget){
                    me.cachedTarget.notifyOut(me, e, me.dragData);
                }
                me.cacheTarget = null;
            }

            if (me.afterInvalidDrop) {
                /**
                 * An empty function by default, but provided so that you can perform a custom action
                 * after an invalid drop has occurred by providing an implementation.
                 * @param {Event} e The event object
                 * @param {String} id The id of the dropped element
                 * @method afterInvalidDrop
                 */
                me.afterInvalidDrop(e, id);
            }
        }
    });