anchor.diff:  ///
   /// The scroll velocity is controlled by the [velocityScalar]:
   ///
  -/// velocity = <distance of overscroll> * [velocityScalar].
  +/// velocity = <distance of overscroll> * [_kDefaultAutoScrollVelocityScalar].
   class _EdgeDraggingAutoScroller {
     /// Creates a auto scroller that scrolls the [scrollable].
  -  _EdgeDraggingAutoScroller(this.scrollable, {this.onScrollViewScrolled, this.velocityScalar = _kDefaultAutoScrollVelocityScalar});
  +  _EdgeDraggingAutoScroller(this.scrollable, {this.onScrollViewScrolled});
   
     // An eyeball value
     static const double _kDefaultAutoScrollVelocityScalar = 7;
  
positive.code:       _scrolling = false;
        return;
      }
      final Duration duration = Duration(milliseconds: (1000 / velocityScalar).round());
      await scrollable.position.animateTo(
        newOffset,
        duration: duration,
  
negative.code:   /// target no longer triggers the auto scroll. This callback will be called
    /// in between each scroll.
    final VoidCallback? onScrollViewScrolled;
  
    late Rect _dragTargetRelatedToScrollOrigin;
  
  