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