anchor.diff:    /// Typically these widgets are [IconButton]s representing common operations.
     /// For less common operations, consider using a [PopupMenuButton] as the
     /// last action.
  -  ///
  -  /// {@tool snippet --template=stateless_widget_material}
  -  ///
  -  /// This sample shows adding an action to an [AppBar] that opens a shopping cart.
  -  ///
  -  /// ```dart
  -  /// Widget build(BuildContext context) {
  -  ///   return Scaffold(
  -  ///     appBar: AppBar(
  -  ///       title: Text('Ready, Set, Shop!'),
  -  ///       actions: <Widget>[
  -  ///         IconButton(
  -  ///           icon: Icon(Icons.shopping_cart),
  -  ///           tooltip: 'Open shopping cart',
  -  ///           onPressed: () {
  -  ///             // Implement navigation to shopping cart page here...
  -  ///             print('Shopping cart opened.');
  -  ///           },
  -  ///         ),
  -  ///       ],
  -  ///     ),
  -  ///   );
  -  /// }
  -  /// ```
  -  /// {@end-tool}
     final List<Widget> actions;
   
     /// This widget is stacked behind the toolbar and the tab bar. It's height will
  
positive.code: /// to false. In that case a null leading widget will result in the middle/title widget
  /// stretching to start.
  ///
  /// {@tool sample}
  ///
  /// ```dart
  /// AppBar(
  ///   title: Text('My Fancy Dress'),
  ///   actions: <Widget>[
  ///     IconButton(
  ///       icon: Icon(Icons.playlist_play),
  ///       tooltip: 'Air it',
  ///       onPressed: _airDress,
  ///     ),
  ///     IconButton(
  ///       icon: Icon(Icons.playlist_add),
  ///       tooltip: 'Restitch it',
  ///       onPressed: _restitchDress,
  ///     ),
  ///     IconButton(
  ///       icon: Icon(Icons.playlist_add_check),
  ///       tooltip: 'Repair it',
  ///       onPressed: _repairDress,
  ///     ),
  ///   ],
  /// )
  /// ```
  /// {@end-tool}
  ///
  
negative.code: import 'text_theme.dart';
  import 'theme.dart';
  
  const double _kLeadingWidth = kToolbarHeight; // So the leading button is square.
  
  // Bottom justify the kToolbarHeight child which may overflow the top.
  