anchor.diff:    /// Returns a new RRect with edges and radii moved outwards by the given
     /// delta.
     RRect inflate(double delta) {
  -    return new RRect.fromLTRBCustom(
  +    return new RRect.fromLTRBAndCorners(
         _value[0] - delta,
         _value[1] - delta,
         _value[2] + delta,
         _value[3] + delta,
  -      new Radius.elliptical(
  +      topLeft: new Radius.elliptical(
           _value[4] + delta,
           _value[5] + delta
         ),
  -      new Radius.elliptical(
  +      topRight: new Radius.elliptical(
           _value[6] + delta,
           _value[7] + delta
         ),
  -      new Radius.elliptical(
  +      bottomRight: new Radius.elliptical(
           _value[8] + delta,
           _value[9] + delta
         ),
  -      new Radius.elliptical(
  +      bottomLeft: new Radius.elliptical(
           _value[10] + delta,
           _value[11] + delta
         )
  
positive.code: 
    /// Returns a new RRect translated by the given offset.
    RRect shift(Offset offset) {
      return new RRect.fromLTRBCustom(
        _value[0] + offset.dx,
        _value[1] + offset.dy,
        _value[2] + offset.dx,
        _value[3] + offset.dy,
        new Radius.elliptical(
          _value[4],
          _value[5]
        ),
        new Radius.elliptical(
          _value[6],
          _value[7]
        ),
        new Radius.elliptical(
          _value[8],
          _value[9]
        ),
        new Radius.elliptical(
          _value[10],
          _value[11]
        )
  
negative.code: 
    /// Construct a rounded rectangle from its bounding box and and topLeft,
    /// topRight, bottomRight, and bottomLeft radii.
    ///
    /// The corner radii default to [Radius.zero], i.e. right-angled corners
    RRect.fromRectAndCorners(
      Rect rect,
      {
        Radius topLeft: Radius.zero,
        Radius topRight: Radius.zero,
        Radius bottomRight: Radius.zero,
        Radius bottomLeft: Radius.zero
      }
    ) {
      _value
        ..[0] = rect.left
        ..[1] = rect.top
  