htmlparser2 convert xml object into string

I'm having a little trouble getting the htmlparser2 module (using node.js) to output an xml string. Basically I'm parsing it in like so:

var htmlparser=require('htmlparser2');
function(xmlString,cb){
    var handler=new htmlparser.DomHandler(cb);
    var parser = new htmlparser.Parser(handler);
    parser.write(xmlString);
    parser.done();
}

Then I get an object called "dom", which I do some work on. After that work is done, I want to export it back into an XML string. I know that htmlparser.DomUtils.getOuterHTML(dom) works for HTML objects, but doesn't work for XML (at least not by default). I get back <undefined></undefined> when I call htmlparser.DomUtils.getOuterHTML(dom) on an xml dom.

Thanks in advance for any help you're able to offer! -Dylan