code: public static void xorCheck(final Nodes nodes1, final Nodes nodes2, final String nodeTypeForDebugging) throws XMLParsingException {
          if (nodes1.size() > 0 && nodes2.size() > 0) {
              throw new XMLParsingException("Message contains more than one " + nodeTypeForDebugging + " node. Only one permitted.");
          }
      }
docs: Does nothing if only one of nodes1 or nodes2 contains more than zero nodes. Throws InvalidCfgDocException otherwise.
  
  @param nodes1
  @param nodes2
  @param nodeTypeForDebugging
  @throws XMLParsingException