anchor.diff:          itemBuilder: _buildItem,
           scrollDirection: widget.scrollDirection,
           physics: widget.scrollPhysics,
  +        allowImplicitScrolling: widget.allowImplicitScrolling,
         ),
       );
     }
  
positive.code: 
    /// The axis along which the [PageView] scrolls. Mirror to [PageView.scrollDirection]
    final Axis scrollDirection;
  
    bool get _isBuilder => builder != null;
  
  
negative.code:     this.scrollPhysics,
      this.scrollDirection = Axis.horizontal,
      this.customSize,
      this.allowImplicitScrolling = false,
    })  : pageOptions = null,
          assert(itemCount != null),
          assert(builder != null),
  