anchor.diff:  
   /// State for a [ScaffoldMessenger].
   ///
  -/// A [ScaffoldMessengerState] object can be used to [showSnackBar] for every
  -/// registered [Scaffold] that is a descendant of the associated
  -/// [ScaffoldMessenger]. Scaffolds will register to receive [SnackBar]s from
  -/// their closest ScaffoldMessenger ancestor.
  +/// A [ScaffoldMessengerState] object can be used to [showSnackBar] or
  +/// [showMaterialBanner] for every registered [Scaffold] that is a descendant of
  +/// the associated [ScaffoldMessenger]. Scaffolds will register to receive
  +/// [SnackBar]s and [MaterialBanner]s from their closest ScaffoldMessenger
  +/// ancestor.
   ///
   /// Typically obtained via [ScaffoldMessenger.of].
   class ScaffoldMessengerState extends State<ScaffoldMessenger> with TickerProviderStateMixin {
  
positive.code:   statusBar,
  }
  
  /// Manages [SnackBar]s for descendant [Scaffold]s.
  ///
  /// This class provides APIs for showing snack bars.
  ///
  /// To display a snack bar, obtain the [ScaffoldMessengerState] for the current
  /// [BuildContext] via [ScaffoldMessenger.of] and use the
  /// [ScaffoldMessengerState.showSnackBar] function.
  ///
  /// When the [ScaffoldMessenger] has nested [Scaffold] descendants, the
  /// ScaffoldMessenger will only present a [SnackBar] to the root Scaffold of
  /// the subtree of Scaffolds. In order to show SnackBars in the inner, nested
  /// Scaffolds, set a new scope for your SnackBars by instantiating a new
  /// ScaffoldMessenger in between the levels of nesting.
  ///
  /// {@tool dartpad --template=stateless_widget_scaffold_center}
  /// Here is an example of showing a [SnackBar] when the user presses a button.
  
negative.code: ///
  ///  * [SnackBar], which is a temporary notification typically shown near the
  ///    bottom of the app using the [ScaffoldMessengerState.showSnackBar] method.
  ///  * [MaterialBanner], which is a temporary notification typically shown at the
  ///    top of the app using the [ScaffoldMessengerState.showMaterialBanner] method.
  ///  * [debugCheckHasScaffoldMessenger], which asserts that the given context
  ///    has a [ScaffoldMessenger] ancestor.
  ///  * Cookbook: [Display a SnackBar](https://flutter.dev/docs/cookbook/design/snackbars)
  