anchor.diff:  
     @override
     void set arguments(ArgumentList arguments) {
  -    _arguments = _becomeParentOf(arguments as AstNodeImpl);
  +    _arguments = _becomeParentOf(arguments as ArgumentListImpl);
     }
   
     @override
  
positive.code:    * and [metadata] can be `null` if the directive does not have the
     * corresponding attribute.
     */
    PartDirectiveImpl(Comment comment, List<Annotation> metadata,
        this.partKeyword, StringLiteral partUri, this.semicolon)
        : super(comment, metadata, partUri);
  
    @override
  
negative.code:   /**
     * The name associated with the expression.
     */
    LabelImpl _name;
  
    /**
     * The expression with which the name is associated.
     */
    ExpressionImpl _expression;
  
    /**
     * Initialize a newly created named expression..
  