code: public void skippedComparison(Node control, Node test) {
          if (differenceListenerDelegate != null) {
              differenceListenerDelegate.skippedComparison(control, test);
          } else {
              System.err.println("DifferenceListener.skippedComparison: "
                                 + "unhandled control node type=" + control
                                 + ", unhandled test node type=" + test);
          }
      }
docs: DifferenceListener implementation.
  If the {@link Diff#overrideDifferenceListener  overrideDifferenceListener}
  method has been called then the call will be delegated
  otherwise a message is printed to <code>System.err</code>.
  @param control
  @param test