int countErrors(int start, int end) {
      int errors = 0;
      if (myBase != null && start < myDeriveIndex) {
        errors += myBase.countErrors(start, myDeriveIndex);
      }

      if (myErrors != null) {
        for (ErrorWithIndex error : myErrors) {
          if (start <= error.index && error.index < end) {
            errors++;
          }
        }
      }

      return errors;
    }
int countErrors(int start, int end)