Sarissa & XML parsing

function callback( responseText)
{
  var oDomDoc = Sarissa.getDomDocument( );

  oDomDoc = ( new DOMParser()).parseFromString( responseText, "text/xml");
  if( oDomDoc.parseError != 0)
    handle_error( ); // or something...

  oDomDoc.setProperty( "SelectionLanguage", "XPath");  //  for IE
  var oElem = oDomDoc.selectSingleNode( "//some_element");
  var str =Sarissa.serialize( oElem);

  ...
}