anchor.diff:    ///
     /// Default is true.
     final bool enableDrag;
  +
  +  /// The z-coordinate at which to place this material. This controls the size
  +  /// of the shadow below the material.
  +  ///
  +  /// Defaults to 0.
  +  final double elevation;
   
     @override
     _BottomSheetState createState() => _BottomSheetState();
  
positive.code:   Widget build(BuildContext context) {
      final Widget bottomSheet = Material(
        key: _childKey,
        child: widget.builder(context),
      );
      return !widget.enableDrag ? bottomSheet : GestureDetector(
  
negative.code:     Key key,
      this.animationController,
      this.enableDrag = true,
      this.elevation = 0.0,
      @required this.onClosing,
      @required this.builder
    }) : assert(enableDrag != null),
         assert(onClosing != null),
         assert(builder != null),
         assert(elevation != null),
         super(key: key);
  
    /// The animation that controls the bottom sheet's position.
  