    /**
     * @class Ext.util.Grouper
     * @extends Ext.util.Sorter
     */

    Ext.define('Ext.util.Grouper', {

        /* Begin Definitions */

        extend: 'Ext.util.Sorter',

        /* End Definitions */

        /**
         * Function description
         * @param {Ext.data.Model} instance The Model instance
         * @return {String} The group string for this model
         */
        getGroupString: function(instance) {
            return instance.get(this.property);
        }
    });