anchor.diff:        this.activeWatchDisposer();
       }
   
  -    this.activeWatchDisposer = this.watch(match[1], (e) {
  -      this.history.replaceState(null, null,
  +    // Automatically update the [url] if the parameters got changed.
  +    this.activeWatchDisposer = this.observe(match[1], (e) {
  +      this.history.replaceState(null, '',
           this.router.routePath(this.activeRoute, e.newValue)
         );
       });
  
positive.code: }
  
  class PageNavigator {
    final watch;
    final History history;
    final Router router;
    final Map<String, dynamic> views;
  
negative.code:   var activeWatchDisposer;
  
    PageNavigator(
      this.observe,
      this.history,
      this.router,
      this.views,
  