anchor.diff:  
     @override
     Token? get requiredKeyword => null;
  +
  +  @override
  +  ChildEntities get _childEntities => ChildEntities()
  +    ..addNode('parameter', parameter)
  +    ..addToken('separator', separator)
  +    ..addNode('defaultValue', defaultValue);
   
     @override
     E? accept<E>(AstVisitor<E> visitor) =>
  
positive.code:   Token get beginToken => leftBracket;
  
    @override
    Iterable<SyntacticEntity> get childEntities => ChildEntities()
      ..add(leftBracket)
      ..addAll(_statements)
      ..add(rightBracket);
  
    @override
    Token get endToken => rightBracket;
  
    @override
    NodeListImpl<Statement> get statements => _statements;
  
    @override
    E? accept<E>(AstVisitor<E> visitor) => visitor.visitBlock(this);
  
negative.code:   set returnType(Identifier typeName) {
      _returnType = _becomeParentOf(typeName as IdentifierImpl);
    }
  
    @override
    ChildEntities get _childEntities => super._childEntities
      ..addToken('externalKeyword', externalKeyword)
      ..addToken('constKeyword', constKeyword)
      ..addToken('factoryKeyword', factoryKeyword)
      ..addNode('returnType', returnType)
      ..addToken('period', period)
      ..addNode('name', name)
      ..addNode('parameters', parameters)
      ..addToken('separator', separator)
      ..addNodeList('initializers', initializers)
      ..addNode('redirectedConstructor', redirectedConstructor)
      ..addNode('body', body);
  
    @override
    E? accept<E>(AstVisitor<E> visitor) =>
  