title: responseType in $.ajax
body: <pre><code>$.ajax({
     type: "POST",
     url: "bla",
     xhrFields: { responseType: "document" },
     data: {},
     success: function(arg,arg2,request){
        console.log(request.responseXML)
     }
  })
  </code></pre>
  
  <p>Why is it printing 'undefined'? How would I fix this?</p>