responseXML.getElementsByTagName() is not implemented in QML (Qt Quick)

responseXML.getElementsByTagName() is not implemented in ECMAScript of QML (Qt Quick)

The code below results in the following error:

.../qml/QtQuickTube/YoutubeDataReader.qml:37: TypeError: Result of expression 'xmlDoc.getElementsByTagName' [undefined] is not a function.

...
xhr.open("GET",url,true);
xhr.onreadystatechange = function() {
  if (xhr.readyState==4) {
    if (xhr.status==200) {
      var xmlDoc=xhr.responseXML;
      var txt="";
      var x=xmlDoc.getElementsByTagName("PARAM");
...

related with bug QTBUG-13987, which "Will be done if it falls out of V8 integration, but otherwise not worth investment."