The source code

    /**
     * @class Ext.data.XmlWriter
     * @extends Ext.data.DataWriter
     * DataWriter extension for writing an array or single {@link Ext.data.Record} object(s) in preparation for executing a remote CRUD action via XML.
     */
    Ext.data.XmlWriter = Ext.extend(Ext.data.DataWriter, {
        /**
         * Final action of a write event.  Apply the written data-object to params.
         * @param {String} action [Ext.data.Api.create|read|update|destroy]
         * @param {Record[]} rs
         * @param {Object} http params
         * @param {Object} data object populated according to DataReader meta-data "root" and "idProperty"
         */
        render : function(action, rs, params, data) {
            // no impl.
        },
        /**
         * createRecord
         * @param {Ext.data.Record} rec
         */
        createRecord : function(rec) {
            // no impl
        },
        /**
         * updateRecord
         * @param {Ext.data.Record} rec
         */
        updateRecord : function(rec) {
            // no impl.

        },
        /**
         * destroyRecord
         * @param {Ext.data.Record} rec
         */
        destroyRecord : function(rec) {
            // no impl
        }
    });