The XML module of the DataType Utility allows you to take an XML document and convert it to a string.
To output an XML document as a string, simply call the format() function of the DataType.XML class:
YUI().use("datatype-xml", function(Y) {
    var xmlString =
        '<myroot>' +
            '<item type="foo">' +
                '<name>Abc</name>' +
                '<rank>1</rank>' +
            '</item>' +
            '<item type="bar">' +
                '<name>Def</name>' +
                '<rank>2</rank>' +
            '</item>' +
            '<item type="bat">' +
                '<name>Ghhi</name>' +
                '<rank>3</rank>' +
            '</item>' +
        '</myroot>';
    var myXMLDoc = Y.DataType.XML.parse(xmlString);
    alert(Y.DataType.XML.format(myXMLDoc));
});