anchor.diff:    final Object tag;
     final Widget child;
     final int turns;
  +
  +  /// If true, the hero will always animate, even if it has no matching hero to
  +  /// animate to or from. (This only applies if the hero is relevant; if there
  +  /// are multiple heroes with the same tag, only the one whose key matches the
  +  /// "most valuable keys" will be used.)
  +  final bool alwaysAnimate;
   
     static Map<Object, HeroHandle> of(BuildContext context, Set<Key> mostValuableKeys) {
       mostValuableKeys ??= new Set<Key>();
  
positive.code: 
    _HeroMode _mode = _HeroMode.constructing;
    Size _size;
  
    _HeroManifest _takeChild(Rect animationArea) {
      assert(_mode == _HeroMode.measured || _mode == _HeroMode.taken);
  
negative.code: }
  
  abstract class HeroHandle {
    bool get alwaysAnimate;
    _HeroManifest _takeChild(Rect animationArea);
  }
  
  