anchor.diff:  }
   
   abstract class HeroHandle {
  +  bool get alwaysAnimate;
     _HeroManifest _takeChild(Rect animationArea);
   }
   
  
positive.code:     final List<_HeroQuestState> _newHeroes = <_HeroQuestState>[];
      for (_HeroMatch heroPair in heroes.values) {
        assert(heroPair.from != null || heroPair.to != null);
        _HeroManifest from = heroPair.from?._takeChild(animationArea);
        assert(heroPair.to == null || heroPair.to is HeroState);
        _HeroManifest to = heroPair.to?._takeChild(animationArea);
  
negative.code:     Key key,
      this.tag,
      this.child,
      this.turns: 1,
      this.alwaysAnimate: false
    }) : super(key: key) {
      assert(tag != null);
    }
  