code: public static void assertXMLValid(InputSource xml, String systemId)
          throws SAXException, ConfigurationException {
          assertXMLValid(new Validator(xml, systemId));
      }
docs: Assert that an InputSource containing XML contains valid XML:
  the document must contain a DOCTYPE to be validated, but the
  validation will use the systemId to obtain the DTD
  @param xml
  @param systemId
  @throws SAXException
  @throws ConfigurationException if validation could not be turned on
  @see Validator