anchor.diff:    /// incoming width constraint multipled by this factor.
     final double widthFactor;
   
  -  /// If non-null, the fraction of the incoming height to give to the child.
  +  /// If non-null, the fraction of the incoming height given to the child.
     ///
     /// If non-null, the child is given a tight height constraint that is the max
     /// incoming height constraint multipled by this factor.
  
positive.code: /// See also:
  ///
  ///  * [Flow]
  ///  * [Align] (which positions a single child according to a [FractionalOffset])
  ///  * [CustomSingleChildLayout]
  ///  * [CustomMultiChildLayout]
  class Stack extends StackRenderObjectWidgetBase {
  
negative.code: /// and the corresponding size factor is null then the widget will match its
  /// child's size in that dimension. If a size factor is non-null then the
  /// corresponding dimension of this widget will be the product of the child's
  /// dimension and the size factor. For example if widthFactor is 2.0 then
  /// the width of this widget will always be twice its child's width.
  ///
  /// See also:
  ///
  ///  * [CustomSingleChildLayout]
  ///  * [Center] (which is the same as [Align] but with the [alignment] always
  ///    set to [FractionalOffset.center])
  ///  * [FractionallySizedBox] (which sizes its child based on a fraction of its own
  ///    size and positions the child according to a [FractionalOffset] value)
  class Align extends SingleChildRenderObjectWidget {
    /// Creates an alignment widget.
    ///
  