code: public Object xpathQuery(String xpath, QName type)
          throws XPathExpressionException {
              return xpathQuery(xpath, type, null);
          }
docs: Return the result of evaluating an XPath query on the builder's DOM.
  Returns null if the query finds nothing,
  or finds a node that does not match the type specified by returnType.
  
  @param xpath
  an XPath expression
  @param type
  the type the XPath is expected to resolve to, e.g:
  {@link XPathConstants#NODE}, {@link XPathConstants#NODESET},
  {@link XPathConstants#STRING}
  
  @return
  a builder node representing the first Element that matches the
  XPath expression.
  
  @throws XPathExpressionException
  If the XPath is invalid, or if does not resolve to at least one
  {@link Node#ELEMENT_NODE}.