[jQuery] Server side JQeury

[howa]

I have been following John's article: 
http://ejohn.org/blog/bringing-the-browser-to-the-server

The script only support well formed XML, as defined in the function
(env.js)

window.__defineSetter__("location", function(url){
                var xhr = new XMLHttpRequest();
                xhr.open("GET", url);
                xhr.onreadystatechange = function(){
                        curLocation = new java.net.URL( curLocation, url );
                        window.document = xhr.responseXML;

                        var event = document.createEvent();
                        event.initEvent("load");
                        window.dispatchEvent( event );
                };
                xhr.send();
        });


But why we need fetch valid XML?