anchor.diff:  /// ```
   /// {@end-tool}
   ///
  +/// {@tool dartpad --template=stateful_widget_material}
  +/// This example shows a [BottomNavigationBar] as it is used within a [Scaffold]
  +/// widget. The [BottomNavigationBar] has four [BottomNavigationBarItem]
  +/// widgets, which means it defaults to [BottomNavigationBarType.shifting], and
  +/// the [currentIndex] is set to index 0. The selected item is amber in color.
  +/// With each [BottomNavigationBarItem] widget, backgroundColor property is
  +/// also defined, which changes the background color of [BottomNavigationBar],
  +/// when that item is selected. The `_onItemTapped` function changes the
  +/// selected item's index and displays a corresponding message in the center of
  +/// the [Scaffold].
  +///
  +///
  +/// ```dart
  +/// int _selectedIndex = 0;
  +/// static const TextStyle optionStyle = TextStyle(fontSize: 30, fontWeight: FontWeight.bold);
  +/// static const List<Widget> _widgetOptions = <Widget>[
  +///   Text(
  +///     'Index 0: Home',
  +///     style: optionStyle,
  +///   ),
  +///   Text(
  +///     'Index 1: Business',
  +///     style: optionStyle,
  +///   ),
  +///   Text(
  +///     'Index 2: School',
  +///     style: optionStyle,
  +///   ),
  +///   Text(
  +///     'Index 3: Settings',
  +///     style: optionStyle,
  +///   ),
  +/// ];
  +///
  +/// void _onItemTapped(int index) {
  +///   setState(() {
  +///     _selectedIndex = index;
  +///   });
  +/// }
  +///
  +/// @override
  +/// Widget build(BuildContext context) {
  +///   return Scaffold(
  +///     appBar: AppBar(
  +///       title: const Text('BottomNavigationBar Sample'),
  +///     ),
  +///     body: Center(
  +///       child: _widgetOptions.elementAt(_selectedIndex),
  +///     ),
  +///     bottomNavigationBar: BottomNavigationBar(
  +///       items: const <BottomNavigationBarItem>[
  +///         BottomNavigationBarItem(
  +///           icon: Icon(Icons.home),
  +///           label: 'Home',
  +///           backgroundColor: Colors.red,
  +///         ),
  +///         BottomNavigationBarItem(
  +///           icon: Icon(Icons.business),
  +///           label: 'Business',
  +///           backgroundColor: Colors.green,
  +///         ),
  +///         BottomNavigationBarItem(
  +///           icon: Icon(Icons.school),
  +///           label: 'School',
  +///           backgroundColor: Colors.purple,
  +///         ),
  +///         BottomNavigationBarItem(
  +///           icon: Icon(Icons.settings),
  +///           label: 'Settings',
  +///           backgroundColor: Colors.pink,
  +///         ),
  +///       ],
  +///       currentIndex: _selectedIndex,
  +///       selectedItemColor: Colors.amber[800],
  +///       onTap: _onItemTapped,
  +///     ),
  +///   );
  +/// }
  +/// ```
  +/// {@end-tool}
   /// See also:
   ///
   ///  * [BottomNavigationBarItem]
  
positive.code: /// {@tool dartpad --template=stateful_widget_material}
  /// This example shows a [BottomNavigationBar] as it is used within a [Scaffold]
  /// widget. The [BottomNavigationBar] has three [BottomNavigationBarItem]
  /// widgets and the [currentIndex] is set to index 0. The selected item is
  /// amber. The `_onItemTapped` function changes the selected item's index
  /// and displays a corresponding message in the center of the [Scaffold].
  ///
  /// ![A scaffold with a bottom navigation bar containing three bottom navigation
  /// bar items. The first one is selected.](https://flutter.github.io/assets-for-api-docs/assets/material/bottom_navigation_bar.png)
  ///
  /// ```dart
  /// int _selectedIndex = 0;
  
negative.code: 
  /// Defines the layout and behavior of a [BottomNavigationBar].
  ///
  /// For a sample on how to use these, please see [BottomNavigationBar].
  /// See also:
  ///
  ///  * [BottomNavigationBar]
  