anchor.diff:    ///       Widget child,
     ///   ) {
     ///     return SlideTransition(
  -  ///       position: AlignmentTween(
  +  ///       position: Tween<Offset>(
     ///         begin: const Offset(0.0, 1.0),
     ///         end: Offset.zero,
     ///       ).animate(animation),
     ///       child: SlideTransition(
  -  ///         position: TweenOffset(
  +  ///         position: Tween<Offset>(
     ///           begin: Offset.zero,
     ///           end: const Offset(0.0, 1.0),
     ///         ).animate(secondaryAnimation),
     ///         child: child,
     ///       ),
  -  ///     );
  -  ///   }
  +  ///      );
  +  ///   },
  +  /// )
     /// ```
  +  /// {@end-tool}
     ///
     /// In practice the `secondaryAnimation` is used pretty rarely.
     ///
  
positive.code:   /// route has been popped off.
    ///
    /// ```dart
    ///   transitionsBuilder: (
    ///       BuildContext context,
    ///       Animation<double> animation,
  
negative.code: // Examples can assume:
  // dynamic routeObserver;
  // late NavigatorState navigator;
  // late BuildContext context;
  // Future<bool> askTheUserIfTheyAreSure() async { return true; }
  // abstract class MyWidget extends StatefulWidget { const MyWidget({Key? key}) : super(key: key); }
  
  /// A route that displays widgets in the [Navigator]'s [Overlay].
  abstract class OverlayRoute<T> extends Route<T> {
  