code: public void overrideMatchTracker(MatchTracker delegate) {
          this.matchTrackerDelegate = delegate;
          if (differenceEngine != null) {
              differenceEngine.setMatchTracker(delegate);
          }
      }
docs: Override the <code>MatchTracker</code> used to track
  successfully matched nodes.
  @param delegate the MatchTracker instance to delegate handling to.