anchor.diff:      fn();
       _scheduleBuild();
     }
  +
  +  String toStringName([String prefix = '', String startPrefix = '']) {
  +    if (_disqualifiedFromEverAppearingAgain)
  +      return '[[DISQUALIFIED]] ${super.toStringName()}';
  +    return super.toStringName();
  +  }
   }
   
   Set<Component> _dirtyComponents = new Set<Component>();
  
positive.code:           } else {
              syncChild(null, oldChild, null);
            }
            oldChildrenBottom -= 1;
          }
        }
      }
  
  
negative.code: 
    void _sync(Widget old, dynamic slot) {
      assert(!_debugChildTaken);
      child = syncChild(child, (old as TagNode)?.child, slot);
      if (child != null) {
        assert(child.parent == this);
        assert(child.renderObject != null);
  