anchor.diff:    }
   
   
  -  remove() {
  +  void remove() {
       _group._recordRemove(this);
     }
   
  -  toString() => '${_MODE_NAMES[_mode]}[$field]';
  +  String toString() => '${_MODE_NAMES[_mode]}[$field]';
   }
   
   final Object _INITIAL_ = new Object();
  
positive.code:   }
  
  
    _check(Map map) {
      _reset();
      _map = map;
      Map records = _records;
  
negative.code:     return record;
    }
  
    void clear() {
      map.clear();
    }
  }
  