anchor.diff:  
     @override
     void set iterable(Expression expression) {
  -    _iterable = _becomeParentOf(expression as AstNodeImpl);
  +    _iterable = _becomeParentOf(expression as ExpressionImpl);
     }
   
     @override
  
positive.code: 
    @override
    void set returnType(TypeAnnotation type) {
      _returnType = _becomeParentOf(type as AstNodeImpl);
    }
  
    @override
  
negative.code:   /**
     * The label associated with the statement, or `null` if there is no label.
     */
    SimpleIdentifierImpl _label;
  
    /**
     * The semicolon terminating the statement.
  