anchor.diff:      _variableList = _becomeParentOf(variableList);
       _initialization = _becomeParentOf(initialization);
       _condition = _becomeParentOf(condition);
  -    _updaters = new NodeList<Expression>(this, updaters);
  +    _updaters = new NodeListImpl<Expression>(this, updaters);
       _body = _becomeParentOf(body);
     }
   
  
positive.code:    */
    ShowCombinatorImpl(Token keyword, List<SimpleIdentifier> shownNames)
        : super(keyword) {
      _shownNames = new NodeList<SimpleIdentifier>(this, shownNames);
    }
  
    @override
  
negative.code:       this.leftDelimiter,
        this.rightDelimiter,
        this.rightParenthesis) {
      _parameters = new NodeListImpl<FormalParameter>(this, parameters);
    }
  
    @override
  