code: public  XObject eval(Node contextNode, String str)
            throws TransformerException
    {
      return eval(contextNode, str, contextNode);
    }
docs: Evaluate XPath string to an XObject.  Using this method,
  XPath namespace prefixes will be resolved from the namespaceNode.
  @param contextNode The node to start searching from.
  @param str A valid XPath string.
  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
  @see org.apache.xpath.objects.XObject
  @see org.apache.xpath.objects.XNull
  @see org.apache.xpath.objects.XBoolean
  @see org.apache.xpath.objects.XNumber
  @see org.apache.xpath.objects.XString
  @see org.apache.xpath.objects.XRTreeFrag
  
  @throws TransformerException