anchor.diff:  
     static XmlNode _renderRSS2(Feed feed) => '';
   
  +  Person author;
     String id;
     String title;
     String description;
     Uri link;
     Uri image;
     String copyright;
  -  String feed;
  -  String hub;
  +  Uri feed;
  +  Uri hub;
     DateTime updated;
  -  String author;
     List<Item> items = [];
     List<String> catagories = [];
  -  List<String> contributors = [];
  +  List<Person> contributors = [];
   
     String toXmlString({
         renderer: FeedRenderer.atom,
  
positive.code:           ..element('title', nest: feed.title);
  
          // Build recommended elements.
          if (feed.link != null) {
            builder.element(
                'link',
                attributes: {'rel': 'alternate'},
                nest: feed.link.toString());
          }
  
          if (feed.feed != null) {
            builder.element(
                'link',
                attributes: {'rel': 'self'},
                nest: feed.feed.toString());
          }
  
          if (feed.hub != null) {
            builder.element(
                'link',
                attributes: {'rel': 'hub'},
                nest: feed.hub.toString());
          }
  
        });
  
negative.code: import 'package:xml/xml.dart';
  
  class Person {
    String name;
    String email;
    Uri link;
  
    Person(this.name, {this.email, this.link});
  }
  
  class Item {
    String title;
  