anchor.diff:                      ),
                     ),
                   ),
  -              ),
  -          ],
  -        ),
  -      );
  +            ],
  +          ),
  +        );
  +      },
  +    );
  +  }
   
     double _cacheExtent(BoxConstraints constraints) => max(
           constraints.maxHeight * _screenScrollCount,
  
positive.code:   }
  
    @override
    Widget build(BuildContext context) => GestureDetector(
          onPanDown: (_) => cancelScrollCallback?.call(),
          excludeFromSemantics: true,
          child: Stack(
            children: <Widget>[
              if (_showBackList)
                PostMountCallback(
                  key: const ValueKey<String>('Back'),
                  callback: startAnimationCallback,
                  child: FadeTransition(
                    opacity: ReverseAnimation(opacity),
                    child: NotificationListener<ScrollNotification>(
                      onNotification: (_) {
                        return scrollNotificationCallback?.call() ==
                            _ListDisplay.back;
                      },
                      child: LayoutBuilder(
                        builder: (context, constraints) => PositionedList(
                          itemBuilder: widget.itemBuilder,
                          separatorBuilder: widget.separatorBuilder,
                          itemCount: widget.itemCount,
  
negative.code:                     ),
                    ),
                  ),
                if (_showFrontList)
                  PostMountCallback(
                    key: const ValueKey<String>('Front'),
                    callback: startAnimationCallback,
                    child: FadeTransition(
                      opacity: opacity,
                      child: NotificationListener<ScrollNotification>(
                        onNotification: (_) {
                          return scrollNotificationCallback?.call() ==
                              _ListDisplay.front;
                        },
                        child: PositionedList(
                          itemBuilder: widget.itemBuilder,
                          separatorBuilder: widget.separatorBuilder,
                          itemCount: widget.itemCount,
  