title: responseType of an XHR is an empty string
body: <p>I just want to retrieve the DOM tree of that <a href="http://satya.kodingen.com/computers.xml" rel="noreferrer">XML</a> with that <a href="http://pastebin.com/egrYEWwi" rel="noreferrer">JS snippet</a>.</p>
  
  <p>I get "undefined" for a.responseXML and I don't know why, because a.responseText contains it, but as string. I found out the responseType is an empty string and I know responseXML is sensible for type.</p>
  
  <p>What I did wrong? </p>