The source code

    /**
     * @class Ext.grid.GridDragZone
     * @extends Ext.dd.DragZone
     * A customized implementation of a {@link Ext.dd.DragZone DragZone} which provides default implementations of two of the
     * template methods of DragZone to enable dragging of the selected rows of a GridPanel.
     * A cooperating {@link Ext.dd.DropZone DropZone} must be created who's template method implementations of
     * {@link Ext.dd.DropZone#onNodeEnter onNodeEnter}, {@link Ext.dd.DropZone#onNodeOver onNodeOver},
     * {@link Ext.dd.DropZone#onNodeOut onNodeOut} and {@link Ext.dd.DropZone#onNodeDrop onNodeDrop} are able
     * to process the {@link #getDragData data} which is provided.
     */
    Ext.grid.GridDragZone = function(grid, config){
        this.view = grid.getView();
        Ext.grid.GridDragZone.superclass.constructor.call(this, this.view.mainBody.dom, config);
        this.scroll = false;
        this.grid = grid;
        this.ddel = document.createElement('div');
        this.ddel.className = 'x-grid-dd-wrap';
    };

    Ext.extend(Ext.grid.GridDragZone, Ext.dd.DragZone, {
        ddGroup : "GridDD",

        /**
         * The provided implementation of the getDragData method which collects the data to be dragged from the GridPanel on mousedown.
         * This data is available for processing in the {@link Ext.dd.DropZone#onNodeEnter onNodeEnter}, {@link Ext.dd.DropZone#onNodeOver onNodeOver},
         * {@link Ext.dd.DropZone#onNodeOut onNodeOut} and {@link Ext.dd.DropZone#onNodeDrop onNodeDrop} methods of a cooperating {@link Ext.dd.DropZone DropZone}.
         * The data object contains the following properties:
         * grid : Ext.Grid.GridPanelThe GridPanel from which the data is being dragged.
         * ddel : htmlElementAn htmlElement which provides the "picture" of the data being dragged.
         * rowIndex : NumberThe index of the row which receieved the mousedown gesture which triggered the drag.
         * selections : ArrayAn Array of the selected Records which are being dragged from the GridPanel.
         *
         */
        getDragData : function(e){
            var t = Ext.lib.Event.getTarget(e);
            var rowIndex = this.view.findRowIndex(t);
            if(rowIndex !== false){
                var sm = this.grid.selModel;
                if(!sm.isSelected(rowIndex) || e.hasModifier()){
                    sm.handleMouseDown(this.grid, rowIndex, e);
                }
                return {grid: this.grid, ddel: this.ddel, rowIndex: rowIndex, selections:sm.getSelections()};
            }
            return false;
        },

        /**
         * The provided implementation of the onInitDrag method. Sets the innerHTML of the drag proxy which provides the "picture"
         * of the data being dragged.
         * The innerHTML data is found by calling the owning GridPanel's {@link Ext.grid.GridPanel#getDragDropText getDragDropText}.
         */
        onInitDrag : function(e){
            var data = this.dragData;
            this.ddel.innerHTML = this.grid.getDragDropText();
            this.proxy.update(this.ddel);
            // fire start drag?
        },

        /**
         * An empty immplementation. Implement this to provide behaviour after a repair of an invalid drop. An implementation might highlight
         * the selected rows to show that they have not been dragged.
         */
        afterRepair : function(){
            this.dragging = false;
        },

        /**
         * An empty implementation. Implement this to provide coordinates for the drag proxy to slide back to after an invalid drop.
         * Called before a repair of an invalid drop to get the XY to animate to.
         * @param {EventObject} e The mouse up event
         * @return {Array} The xy location (e.g. [100, 200])
         */
        getRepairXY : function(e, data){
            return false;
        },

        onEndDrag : function(data, e){
            // fire end drag?
        },

        onValidDrop : function(dd, e, id){
            // fire drag drop?
            this.hideProxy();
        },

        beforeInvalidDrop : function(e, id){

        }
    });