anchor.diff:    ///
     /// Since a zero width is normally painted as a hairline width rather than no
     /// border at all, the zero factor is special-cased to instead change the
  -  /// style no [BorderStyle.none].
  +  /// style to [BorderStyle.none].
     ///
     /// Values for `t` are usually obtained from an [Animation<double>], such as
     /// an [AnimationController].
  
positive.code: ///
  /// A [Border] consists of four [BorderSide] objects: [Border.top],
  /// [Border.left], [Border.right], and [Border.bottom].
  ///
  /// {@tool sample}
  ///
  
negative.code:   /// The color of this side of the border.
    final Color color;
  
    /// The width of this side of the border, in logical pixels.
    ///
    /// Setting width to 0.0 will result in a hairline border. This means that
    /// the border will have the width of one physical pixel. Also, hairline
    /// rendering takes shortcuts when the path overlaps a pixel more than once.
    /// This means that it will render faster than otherwise, but it might
    /// double-hit pixels, giving it a slightly darker/lighter result.
    ///
    /// To omit the border entirely, set the [style] to [BorderStyle.none].
    final double width;
  
    /// The style of this side of the border.
  