anchor.diff:  /// to false. In that case a null leading widget will result in the middle/title widget
   /// stretching to start.
   ///
  -/// {@tool sample}
  +/// {@tool snippet --template=stateless_widget_material}
  +///
  +/// This sample shows an [AppBar] with two simple actions. The first action
  +/// opens a [SnackBar], while the second action navigates to a new page.
  +///
  +/// ```dart preamble
  +/// final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
  +/// final SnackBar snackBar = const SnackBar(content: Text('Showing Snackbar'));
  +///
  +/// void openPage(BuildContext context) {
  +///   Navigator.push(context, MaterialPageRoute(
  +///     builder: (BuildContext context) {
  +///       return Scaffold(
  +///         appBar: AppBar(
  +///           title: const Text('Next page'),
  +///         ),
  +///         body: const Center(
  +///           child: Text(
  +///             'This is the next page',
  +///             style: TextStyle(fontSize: 24),
  +///           ),
  +///         ),
  +///       );
  +///     },
  +///   ));
  +/// }
  +/// ```
   ///
   /// ```dart
  -/// AppBar(
  -///   title: Text('My Fancy Dress'),
  -///   actions: <Widget>[
  -///     IconButton(
  -///       icon: Icon(Icons.playlist_play),
  -///       tooltip: 'Air it',
  -///       onPressed: _airDress,
  +/// Widget build(BuildContext context) {
  +///   return Scaffold(
  +///     key: scaffoldKey,
  +///     appBar: AppBar(
  +///       title: const Text('AppBar Demo'),
  +///       actions: <Widget>[
  +///         IconButton(
  +///           icon: const Icon(Icons.add_alert),
  +///           tooltip: 'Show Snackbar',
  +///           onPressed: () {
  +///             scaffoldKey.currentState.showSnackBar(snackBar);
  +///           },
  +///         ),
  +///         IconButton(
  +///           icon: const Icon(Icons.navigate_next),
  +///           tooltip: 'Next page',
  +///           onPressed: () {
  +///             openPage(context);
  +///           },
  +///         ),
  +///       ],
   ///     ),
  -///     IconButton(
  -///       icon: Icon(Icons.playlist_add),
  -///       tooltip: 'Restitch it',
  -///       onPressed: _restitchDress,
  +///     body: const Center(
  +///       child: Text(
  +///         'This is the home page',
  +///         style: TextStyle(fontSize: 24),
  +///       ),
   ///     ),
  -///     IconButton(
  -///       icon: Icon(Icons.playlist_add_check),
  -///       tooltip: 'Repair it',
  -///       onPressed: _repairDress,
  -///     ),
  -///   ],
  -/// )
  +///   );
  +/// }
   /// ```
   /// {@end-tool}
   ///
  
positive.code: import 'text_theme.dart';
  import 'theme.dart';
  
  // Examples can assume:
  // void _airDress() { }
  // void _restitchDress() { }
  // void _repairDress() { }
  
  const double _kLeadingWidth = kToolbarHeight; // So the leading button is square.
  
  // Bottom justify the kToolbarHeight child which may overflow the top.
  
negative.code:   /// Typically these widgets are [IconButton]s representing common operations.
    /// For less common operations, consider using a [PopupMenuButton] as the
    /// last action.
    final List<Widget> actions;
  
    /// This widget is stacked behind the toolbar and the tab bar. It's height will
  