anchor.diff:  /// class Bird extends StatefulWidget {
   ///   const Bird({
   ///     Key key,
  -///     this.color: const Color(0xFFFFE306),
  +///     this.color = const Color(0xFFFFE306),
   ///     this.child,
   ///   }) : super(key: key);
   ///
   ///   final Color color;
  -///
   ///   final Widget child;
   ///
   ///   _BirdState createState() => _BirdState();
  
positive.code: ///
  /// {@tool sample}
  ///
  /// The following is a skeleton of a stateful widget subclass called `YellowBird`:
  ///
  /// ```dart
  /// class YellowBird extends StatefulWidget {
  
negative.code: /// {@end-tool}
  /// {@tool sample}
  ///
  /// This example shows the more generic widget `Bird` which can be given a
  /// color and a child, and which has some internal state with a method that
  /// can be called to mutate it:
  ///
  