code: public int differenceFound(Difference difference) {
          final int returnValue = super.differenceFound(difference);
          switch (returnValue) {
          case RETURN_IGNORE_DIFFERENCE_NODES_IDENTICAL:
              return returnValue;
          case RETURN_ACCEPT_DIFFERENCE:
              break;
          case RETURN_IGNORE_DIFFERENCE_NODES_SIMILAR:
              difference.setRecoverable(true);
              break;
          case RETURN_UPGRADE_DIFFERENCE_NODES_DIFFERENT:
              difference.setRecoverable(false);
              break;
          default:
              throw new IllegalArgumentException(returnValue
                                                 + " is not a defined "
                                                 + " DifferenceListener"
                                                 + ".RETURN_... value");
          }
          allDifferences.add(difference);
          return returnValue;
      }
docs: DifferenceListener implementation.
  Add the difference to the list of all differences
  @param difference
  @return the value supplied by the superclass implementation