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:   /// Otherwise, the width argument should be ignored, and the returned value
    /// should be equal to or bigger than the value returned by
    /// [computeMinIntrinsicHeight].
    ///
    /// The value returned by this method might not match the size that the object
    /// would actually take. For example, a [RenderBox] subclass that always
  
negative.code:   /// decreases the preferred height. The preferred height is the value that
    /// would be returned by [getMinIntrinsicHeight] for that width.
    ///
    /// The height argument may give a specific height to assume. The given height
    /// can be infinite, meaning that the intrinsic width in an unconstrained
    /// environment is being requested. The given height 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]).
  