code: private static void parseUnrecognizedElement(final Object instance,
                                          final Element element,
                                          final Properties props) throws Exception {
        boolean recognized = false;
        if (instance instanceof UnrecognizedElementHandler) {
            recognized = ((UnrecognizedElementHandler) instance).parseUnrecognizedElement(
                    element, props);
        }
        if (!recognized) {
            LogLog.warn("Unrecognized element " + element.getNodeName());
        }
    }
docs: Delegates unrecognized content to created instance if
  it supports UnrecognizedElementParser.
  @since 1.2.15
  @param instance instance, may be null.
  @param element element, may not be null.
  @param props properties
  @throws IOException thrown if configuration of owner object
  should be abandoned.