title: google maps js v3 xml is null
body: <p>Im trying to retrieve the XML and put it into the var markers, when I run it the line </p>
  
  <pre><code>var markers = xml.documentElement.getElementsByTagName("marker");
  </code></pre>
  
  <p>I get an error saying XML is null, here is the XML I get when running the file that produces the XML</p>
  
  <pre><code>This XML file does not appear to have any style information associated with it. The document tree is shown below.
    &lt;markers&gt;
   &lt;marker name="funtimes" address="5451 Forest Cove Lane" lat="34.1519" lng="-118.774717" type="Basketball" desc="going to play fun times with fun people" date="2012-12-29" time="23:00:00" eventcap="4" eventcur="10" eventid="1" admin="true"/&gt;
   &lt;marker name="Event test" address="1231 fake st" lat="34.1517" lng="-118.77234" type="Cycling" desc="just a description" date="2013-01-31" time="12:00:00" eventcap="10" eventcur="4" eventid="2" admin="true"/&gt;
   &lt;marker name="Event test 2" address="1231 fake st" lat="34.1512" lng="-118.77421" type="Football" desc="just a description 2" date="2013-01-31" time="12:00:00" eventcap="10" eventcur="3" eventid="3" admin="true"/&gt;
   &lt;marker name="funtimes" address="5451 Forest Cove Lane" lat="34.1519" lng="-118.774717" type="Basketball" desc="going to play fun times with fun people" date="2012-12-29" time="23:00:00" eventcap="4" eventcur="10" eventid="1" admin="false"/&gt;    
   &lt;marker name="Event test" address="1231 fake st" lat="34.1517" lng="-118.77234" type="Cycling" desc="just a description" date="2013-01-31" time="12:00:00" eventcap="10" eventcur="4" eventid="2" admin="false"/&gt;
   &lt;marker name="Event test 2" address="1231 fake st" lat="34.1512" lng="-118.77421" type="Football" desc="just a description 2" date="2013-01-31" time="12:00:00" eventcap="10" eventcur="3" eventid="3" admin="false"/&gt;
   &lt;marker name="Event test 3" address="2142 fake st" lat="34.1602" lng="-118.77789" type="Football" desc="just a description 3" date="2013-01-28" time="13:00:00" eventcap="8" eventcur="2" eventid="4" admin="false"/&gt;
   &lt;/markers&gt;
  </code></pre>
  
  <p>Here is some of the surrounding code</p>
  
  <pre><code>downloadUrl("mapXML2.php", function(data) {
  var xml = data.responseXML;
  var markers = xml.documentElement.getElementsByTagName("marker");
  
   function downloadUrl(url, callback) {
        var request = window.ActiveXObject ?
        new ActiveXObject('Microsoft.XMLHTTP') :
        new XMLHttpRequest;
  
    request.onreadystatechange = function() {
      if (request.readyState == 4) {
        request.onreadystatechange = doNothing;
        callback(request, request.status);
      }
    };
  
    request.open('GET', url, true);
    request.send(null);
  }
  </code></pre>