anchor.diff:              ]
             )
           ],
  -        // This empty space keeps the app bar from moving until the screen is
  -        // scrolled at least _getAppBarHeight().
  -        flexibleSpace: new Container()
         ),
         body: _buildContainer(context)
       );
  
positive.code:       scrollableKey: _scrollableKey,
        appBarBehavior: AppBarBehavior.scroll,
        appBar: new AppBar(
          expandedHeight: _getAppBarHeight(context),
          backgroundColor: Colors.transparent,
          elevation: 0,
  
negative.code:   final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
    final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
    final TextStyle menuItemStyle = new PestoStyle(fontSize: 15.0, color: Colors.black54, height: 24.0/15.0);
    final Object _disableHeroTransition = new Object();
  
    double _getAppBarHeight(BuildContext context) => MediaQuery.of(context).size.height * 0.3;
  
  