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:     return record;
    }
  
    void clear() => map.clear();
  }
  
negative.code:     }
    }
  
    Iterable get iterable => _iterable;
  
    bool _check(Iterable collection) {
      _reset();
      ItemRecord record = _collectionHead;
      bool maybeDirty = false;
  