anchor.diff:    operator[](String key);
   }
   
  -class _GlobalViewImpl extends ChangeNotifier implements GlobalView, Map {
  +class _GlobalViewImpl extends ChangeNotifier with _FakeMap implements GlobalView {
   
     EntityWrapper _entity;
     Map<String, GlobalRegistration> _globals;
  
positive.code: }
  
  /// A [GlobalView] for an [Entity] that does not have globals.
  class _EmptyGlobalView implements GlobalView {
  
    static const _singleton = const _EmptyGlobalView._useFactoryInstead();
  
  
negative.code:   }
  }
  
  abstract class _FakeMap {
    get isEmpty => throw "Not implemented";
    get isNotEmpty => throw "Not implemented";
    get keys => throw "Not implemented";
    get values => throw "Not implemented";
    get length => throw "Not implemented";
    operator[]=(_a, _b) => throw "Not implemented";
    addAll(_) => throw "Not implemented";
    clear() => throw "Not implemented";
    containsValue(_) => throw "Not implemented";
    forEach(_) => throw "Not implemented";
    putIfAbsent(_a, _b) => throw "Not implemented";
    remove(_) => throw "Not implemented";
  }
  
  /// A view of globals as they relate to a specific [Entity]. Implements
  /// observability based on dependencies of the globals involved.
  abstract class GlobalView extends Observable with _FakeMap implements Map {
    /// A real global view backed by a map of registered globals.
    factory GlobalView(EntityWrapper entity,
        Map<String, GlobalRegistration> globals) =>
  