anchor.diff:  
     void _remove(OverlayEntry entry) {
       if (mounted) {
  -      _entries.remove(entry);
  -      setState(() { /* entry was removed */ });
  +      setState(() {
  +        _entries.remove(entry);
  +      });
       }
     }
   
  
positive.code: /// [offstage] widgets which are kept alive, and are built, but are not laid out
  /// or painted.
  ///
  /// The onstage widget must be a Stack.
  ///
  /// For convenience, it is legal to use [Positioned] widgets around the offstage
  /// widgets.
  
negative.code: 
    /// The state from the closest instance of this class that encloses the given context.
    ///
    /// In debug mode, if the `debugRequiredFor` argument is provided then this
    /// function will assert that an overlay was found and will throw an exception
    /// if not. The exception attempts to explain that the calling [Widget] (the
    /// one given by the `debugRequiredFor` argument) needs an [Overlay] to be
    /// present to function.
    ///
    /// Typical usage is as follows:
  