code: public static void assertXMLValid(String xmlString, String systemId, String doctype)
          throws SAXException, ConfigurationException {
          assertXMLValid(new Validator(new StringReader(xmlString), systemId, doctype));
      }
docs: Assert that a String containing XML contains valid XML: the String will
  be given a DOCTYPE to be validated with the name and systemId specified
  regardless of whether it already contains a doctype declaration.
  @param xmlString
  @param systemId
  @param doctype
  @throws SAXException
  @throws ConfigurationException if validation could not be turned on
  @see Validator