anchor.diff:    }
   
     void forEach(void f(Node element)) => _toList().forEach(f);
  +
  +  Collection map(f(Node element)) {
  +    List output = new List();
  +    forEach((Node element) {
  +        output.add(f(element));
  +    });
  +    return output;
  +  }
   
     Collection<Node> filter(bool f(Node element)) {
       List<Node> output = new List<Node>();
  
positive.code:     return last;
    }
  
    Collection<Element> filter(bool f(Element element)) => _filtered.filter(f);
    bool every(bool f(Element element)) => _filtered.every(f);
    bool some(bool f(Element element)) => _filtered.some(f);
  
negative.code:     _read().forEach(f);
    }
  
    Collection map(f(String element)) {
      return _read().map(f);
    }
  
    Collection<String> filter(bool f(String element)) {
      return _read().filter(f);
    }
  