anchor.diff:  
     /// Construct a rounded rectangle from its left, top, right, and bottom edges,
     /// and topLeft, topRight, bottomRight, and bottomLeft radii.
  -  RRect.fromLTRBCustom(double left, double top, double right, double bottom,
  -                      Radius topLeft, Radius topRight, Radius bottomRight,
  -                      Radius bottomLeft) {
  +  ///
  +  /// The corner radii default to [Radius.zero], i.e. right-angled corners.
  +  RRect.fromLTRBAndCorners(
  +    double left,
  +    double top,
  +    double right,
  +    double bottom,
  +    {
  +      Radius topLeft: Radius.zero,
  +      Radius topRight: Radius.zero,
  +      Radius bottomRight: Radius.zero,
  +      Radius bottomLeft: Radius.zero
  +    }
  +  ) {
       _value
         ..[0] = left
         ..[1] = top
  
positive.code: 
    /// Construct a rounded rectangle from its bounding box and and topLeft,
    /// topRight, bottomRight, and bottomLeft radii.
    RRect.fromRectCustom(Rect rect, Radius topLeft, Radius topRight,
                        Radius bottomRight, Radius bottomLeft) {
      _value
        ..[0] = rect.left
        ..[1] = rect.top
  
negative.code: 
    @override
    String toString() {
      return 'RRect.fromLTRBAndCorners(${left.toStringAsFixed(1)}, '
          '${top.toStringAsFixed(1)}, ${right.toStringAsFixed(1)}, '
          '${bottom.toStringAsFixed(1)}, '
          'topLeft: $tlRadius, topRight: $trRadius, '
          'bottomRight: $brRadius, bottomLeft: $blRadius)';
    }
  }
  
  