anchor.diff:    /// width-in-height-out when the height is unconstrained, then the width
     /// argument is the width to use.
     ///
  +  /// The `width` argument will never be negative or null. It may be infinite.
  +  ///
     /// If this algorithm depends on the intrinsic dimensions of a child, the
     /// intrinsic dimensions of that child should be obtained using the functions
     /// whose names start with `get`, not `compute`.
  
positive.code:   /// [computeMaxIntrinsicWidth].
    @mustCallSuper
    double getMaxIntrinsicWidth(double height) {
      return _computeIntrinsicDimension(_IntrinsicDimension.maxWidth, height, computeMaxIntrinsicWidth);
    }
  
  
negative.code:   /// decreases the preferred width. The preferred width is the value that
    /// would be returned by [getMinIntrinsicWidth] for that height.
    ///
    /// The width argument may give a specific width to assume. The given width
    /// can be infinite, meaning that the intrinsic height in an unconstrained
    /// environment is being requested. The given width should never be negative
    /// or null.
    ///
    /// This function should only be called on one's children. Calling this
    /// function couples the child with the parent so that when the child's layout
    /// changes, the parent is notified (via [markNeedsLayout]).
  