anchor.diff:    /// route. The type of `result`, if provided, must match the type argument of
     /// the class of the current route. (In practice, this is usually "dynamic".)
     ///
  -  /// Returns a Future that completes when the pushed route is popped.
  +  /// Returns a [Future] that completes to the `result` value passed to [pop]
  +  /// when the pushed route is popped off the navigator.
     ///
     /// Typical usage is as follows:
     ///
  
positive.code:     return Navigator.of(context).pushNamed(routeName);
    }
  
    /// Push a route onto the navigator that most tightly encloses the given context.
    ///
    /// Adds the given route to the Navigator's history, and transitions to it.
    /// The route will have didPush() and didChangeNext() called on it; the
    /// previous route, if any, will have didChangeNext() called on it; and the
    /// Navigator observer, if any, will have didPush() called on it.
    ///
    /// Returns a Future that completes when the pushed route is popped.
    static Future<dynamic> push(BuildContext context, Route<dynamic> route) {
      return Navigator.of(context).push(route);
    }
  
negative.code: 
    bool _debugLocked = false; // used to prevent re-entrant calls to push, pop, and friends
  
    /// Push a named route onto the navigator.
    ///
    /// The route name will be passed to [Navigator.onGenerateRoute]. The returned
    /// route will be pushed into the navigator.
    ///
    /// Returns a [Future] that completes to the `result` value passed to [pop]
    /// when the pushed route is popped off the navigator.
    ///
    /// Typical usage is as follows:
    ///
    /// ```dart
    /// Navigator.of(context).pushNamed('/nyc/1776');
    /// ```
    Future<dynamic> pushNamed(String name) {
      assert(!_debugLocked);
      assert(name != null);
  