anchor.diff:    static const int _kHasCheckedStateIndex = 1 << 0;
     static const int _kIsCheckedIndex = 1 << 1;
     static const int _kIsSelectedIndex = 1 << 2;
  -  static const int _kIsButton = 1 << 3;
  +  static const int _kIsButtonIndex = 1 << 3;
   
     const SemanticsFlags._(this.index);
   
  
positive.code:     _kHasCheckedStateIndex: hasCheckedState,
      _kIsCheckedIndex: isChecked,
      _kIsSelectedIndex: isSelected,
    };
  
    @override
  
negative.code:   /// Platforms has special handling for buttons, for example Android's TalkBack
    /// and iOS's VoiceOver provides an additional hint when the focused object is
    /// a button.
    static const SemanticsFlags isButton = const SemanticsFlags._(_kIsButtonIndex);
  
    /// The possible semantics flags.
    ///
  