anchor.diff:  
     /// Called when this object is inserted into the tree.
     ///
  +  /// The framework will call this method exactly once for each [State] object
  +  /// it creates.
  +  ///
     /// Override this method to perform initialization that depends on the
     /// location at which this object was inserted into the tree (i.e., [context])
  -  /// or on the widget used to configure this object (i.e., [config])
  -  ///
  -  /// The framework will call this method exactly once for each [State] object
  -  /// it creates.
  +  /// or on the widget used to configure this object (i.e., [config]).
  +  ///
  +  /// If a [State]'s [build] method depends on an object that can itself change
  +  /// state, for example a [ChangeNotifier] or [Stream], or some other object to
  +  /// which one can subscribe to receive notifications, then the [State] should
  +  /// subscribe to that object during [initState], unsubscribe from the old
  +  /// object and subscribe to the new object when it changes in
  +  /// [didUpdateConfig], and then unsubscribe from the object in [dispose].
     ///
     /// You cannot use [BuildContext.inheritFromWidgetOfExactType] from this
     /// method. However, [dependenciesChanged] will be called immediately
  
positive.code:   /// refer to the new widget and then call the this method with the previous
    /// widget as an argument.
    ///
    /// Override this metthod to respond to changes in the [config] widget (e.g.,
    /// to start implicit animations).
    ///
    /// The framework always calls [build] after calling [didUpdateConfig], which
    /// means any calls to [setState] in [didUpdateConfig] are redundant.
    ///
    /// If you override this, make sure your method starts with a call to
    /// super.didUpdateConfig(oldConfig).
  
negative.code: ///
  /// See also:
  ///
  ///  * [StatefulWidget], where the current configuration of a [State] is hosted
  ///    (see [config]).
  ///  * [StatelessWidget], for widgets that always build the same way given a
  ///    particular configuration and ambient state.
  ///  * [InheritedWidget], for widgets that introduce ambient state that can
  ///    be read by descendant widgets.
  @optionalTypeArgs
  abstract class State<T extends StatefulWidget> {
    /// The current configuration.
  