anchor.diff:    void appendElementsTo(Element root) {
       this._elements().forEach((element) => root.append(element));
     }
  -
  -  /// Returns a button element that moves the app to the next state.
  -  ///
  -  /// Both concrete States needed this common code so it was pulled up.
  -  Element button() {
  -    Element button = new ButtonElement();
  -    button.text = "click";
  -    button.onClick.listen((e) => app.displayNextState());
  -    return button;
  -  }
   }
   
   /// Represents the state of the app when it is displaying the question
  
positive.code:   State nextState() {
      return new StartState();
    }
  }
  
  /// Represents the visual app in front of the user.
  
negative.code:   List<Element> _elements() {
      return [
        this._currentDrill.questionDiv(),
        new NextStateButton().element()
        ];
    }
  
  