code: public XObject execute(
            XPathContext xctxt, org.w3c.dom.Node contextNode, 
            PrefixResolver namespaceContext)
              throws javax.xml.transform.TransformerException
    {
      return execute(
            xctxt, xctxt.getDTMHandleFromNode(contextNode), 
            namespaceContext);
    }
docs: Given an expression and a context, evaluate the XPath
  and return the result.
  
  @param xctxt The execution context.
  @param contextNode The node that "." expresses.
  @param namespaceContext The context in which namespaces in the
  XPath are supposed to be expanded.
  
  @return The result of the XPath or null if callbacks are used.
  @throws TransformerException thrown if
  the error condition is severe enough to halt processing.
  
  @throws javax.xml.transform.TransformerException
  @xsl.usage experimental