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.
     * XmlWriter uses an instance of {@link Ext.XTemplate} for maximum flexibility in defining your own custom XML schema if the default schema is not appropriate for your needs.
     * See the {@link #tpl} configuration-property.
     */
    Ext.data.XmlWriter = function(params) {
        Ext.data.XmlWriter.superclass.constructor.apply(this, arguments);
        // compile the XTemplate for rendering XML documents.
        this.tpl = (typeof(this.tpl) === 'string') ? new Ext.XTemplate(this.tpl).compile() : this.tpl.compile();
    };
    Ext.extend(Ext.data.XmlWriter, Ext.data.DataWriter, {
        /**
         * @cfg {String} documentRoot [xrequest] (Optional) The name of the XML document root-node.  <b>Note:</b>
         * this parameter is required </b>only when</b> sending extra {@link Ext.data.Store#baseParams baseParams} to the server
         * during a write-request -- if no baseParams are set, the {@link Ext.data.XmlReader#record} meta-property can
         * suffice as the XML document root-node for write-actions involving just a <b>single record</b>.  For requests
         * involving <b>multiple</b> records and <b>NO</b> baseParams, the {@link Ext.data.XmlWriter#root} property can
         * act as the XML document root.
         */
        documentRoot: 'xrequest',
        /**
         * @cfg {Boolean} forceDocumentRoot [false] Set to <tt>true</tt> to force XML documents having a root-node as defined
         * by {@link #documentRoot}, even with no baseParams defined.
         */
        forceDocumentRoot: false,
        /**
         * @cfg {String} root [records] The name of the containing element which will contain the nodes of an write-action involving <b>multiple</b> records.  Each
         * xml-record written to the server will be wrapped in an element named after {@link Ext.data.XmlReader#record} property.
         * eg:
    <code><pre>
    &lt;?xml version="1.0" encoding="UTF-8"?>
    &lt;user>&lt;first>Barney&lt;/first>&lt;/user>
    </code></pre>
         * However, when <b>multiple</b> records are written in a batch-operation, these records must be wrapped in a containing
         * Element.
         * eg:
    <code><pre>
    &lt;?xml version="1.0" encoding="UTF-8"?>
        &lt;records>
            &lt;first>Barney&lt;/first>&lt;/user>
            &lt;records>&lt;first>Barney&lt;/first>&lt;/user>
        &lt;/records>
    </code></pre>
         * Defaults to <tt>records</tt>.  Do not confuse the nature of this property with that of {@link #documentRoot}
         */
        root: 'records',
        /**
         * @cfg {String} xmlVersion [1.0] The <tt>version</tt> written to header of xml documents.
    <code><pre>&lt;?xml version="1.0" encoding="ISO-8859-15"?></pre></code>
         */
        xmlVersion : '1.0',
        /**
         * @cfg {String} xmlEncoding [ISO-8859-15] The <tt>encoding</tt> written to header of xml documents.
    <code><pre>&lt;?xml version="1.0" encoding="ISO-8859-15"?></pre></code>
         */
        xmlEncoding: 'ISO-8859-15',
        /**
         * @cfg {String/Ext.XTemplate} tpl The XML template used to render {@link Ext.data.Api#actions write-actions} to your server.
         * <p>One can easily provide his/her own custom {@link Ext.XTemplate#constructor template-definition} if the default does not suffice.</p>
         * <p>Defaults to:</p>
    <code><pre>
    &lt;?xml version="{version}" encoding="{encoding}"?>
        &lt;tpl if="documentRoot">&lt;{documentRoot}>
        &lt;tpl for="baseParams">
            &lt;tpl for=".">
                &lt;{name}>{value}&lt;/{name}>
            &lt;/tpl>
        &lt;/tpl>
        &lt;tpl if="records.length &gt; 1">&lt;{root}>',
        &lt;tpl for="records">
            &lt;{parent.record}>
            &lt;tpl for=".">
                &lt;{name}>{value}&lt;/{name}>
            &lt;/tpl>
            &lt;/{parent.record}>
        &lt;/tpl>
        &lt;tpl if="records.length &gt; 1">&lt;/{root}>&lt;/tpl>
        &lt;tpl if="documentRoot">&lt;/{documentRoot}>&lt;/tpl>
    </pre></code>
         * <p>Templates will be called with the following API</p>
         * <ul>
         * <li>{String} version [1.0] The xml version.</li>
         * <li>{String} encoding [ISO-8859-15] The xml encoding.</li>
         * <li>{String/false} documentRoot The XML document root-node name or <tt>false</tt> if not required.  See {@link #documentRoot} and {@link #forceDocumentRoot}.</li>
         * <li>{String} record The meta-data parameter defined on your {@link Ext.data.XmlReader#record} configuration represents the name of the xml-tag containing each record.</li>
         * <li>{String} root The meta-data parameter defined by {@link Ext.data.XmlWriter#root} configuration-parameter.  Represents the name of the xml root-tag when sending <b>multiple</b> records to the server.</li>
         * <li>{Array} records The records being sent to the server, ie: the subject of the write-action being performed.  The records parameter will be always be an array, even when only a single record is being acted upon.
         *     Each item within the records array will contain an array of field objects having the following properties:
         *     <ul>
         *         <li>{String} name The field-name of the record as defined by your {@link Ext.data.Record#create Ext.data.Record definition}.  The "mapping" property will be used, otherwise it will match the "name" property.  Use this parameter to define the XML tag-name of the property.</li>
         *         <li>{Mixed} value The record value of the field enclosed within XML tags specified by name property above.</li>
         *     </ul></li>
         * <li>{Array} baseParams.  The baseParams as defined upon {@link Ext.data.Store#baseParams}.  Note that the baseParams have been converted into an array of [{name : "foo", value: "bar"}, ...] pairs in the same manner as the <b>records</b> parameter above.  See {@link #documentRoot} and {@link #forceDocumentRoot}.</li>
         * </ul>
         */
        // Encoding the ? here in case it's being included by some kind of page that will parse it (eg. PHP)
        tpl: '<tpl for="."><\u003fxml version="{version}" encoding="{encoding}"\u003f><tpl if="documentRoot"><{documentRoot}><tpl for="baseParams"><tpl for="."><{name}>{value}</{name}></tpl></tpl></tpl><tpl if="records.length&gt;1"><{root}></tpl><tpl for="records"><{parent.record}><tpl for="."><{name}>{value}</{name}></tpl></{parent.record}></tpl><tpl if="records.length&gt;1"></{root}></tpl><tpl if="documentRoot"></{documentRoot}></tpl></tpl>',

        /**
         * XmlWriter implementation of the final stage of a write action.
         * @param {Object} params Transport-proxy's (eg: {@link Ext.Ajax#request}) params-object to write-to.
         * @param {Object} baseParams as defined by {@link Ext.data.Store#baseParams}.  The baseParms must be encoded by the extending class, eg: {@link Ext.data.JsonWriter}, {@link Ext.data.XmlWriter}.
         * @param {Object/Object[]} data Data-object representing the compiled Store-recordset.
         */
        render : function(params, baseParams, data) {
            baseParams = this.toArray(baseParams);
            params.xmlData = this.tpl.applyTemplate({
                version: this.xmlVersion,
                encoding: this.xmlEncoding,
                documentRoot: (baseParams.length > 0 || this.forceDocumentRoot === true) ? this.documentRoot : false,
                record: this.meta.record,
                root: this.root,
                baseParams: baseParams,
                records: (Ext.isArray(data[0])) ? data : [data]
            });
        },

        /**
         * createRecord
         * @protected
         * @param {Ext.data.Record} rec
         * @return {Array} Array of <tt>name:value</tt> pairs for attributes of the {@link Ext.data.Record}.  See {@link Ext.data.DataWriter#toHash}.
         */
        createRecord : function(rec) {
            return this.toArray(this.toHash(rec));
        },

        /**
         * updateRecord
         * @protected
         * @param {Ext.data.Record} rec
         * @return {Array} Array of {name:value} pairs for attributes of the {@link Ext.data.Record}.  See {@link Ext.data.DataWriter#toHash}.
         */
        updateRecord : function(rec) {
            return this.toArray(this.toHash(rec));

        },
        /**
         * destroyRecord
         * @protected
         * @param {Ext.data.Record} rec
         * @return {Array} Array containing a attribute-object (name/value pair) representing the {@link Ext.data.DataReader#idProperty idProperty}.
         */
        destroyRecord : function(rec) {
            var data = {};
            data[this.meta.idProperty] = rec.id;
            return this.toArray(data);
        }
    });