anchor.diff:    /// registered.
     ///
     /// See also:
  +  ///
     ///  * [addAction] to add an action.
     VoidCallback getActionHandler(SemanticsAction action) => _actions[action];
   
  
positive.code:   /// would like to contribute to the semantics tree.
    ///
    /// See also:
    /// * [addAction] to add an action.
    final Map<SemanticsAction, VoidCallback> _actions = <SemanticsAction, VoidCallback>{};
  
  
negative.code:   /// decedent nodes are merged into this node.
    ///
    /// See also:
    ///
    ///  * [isMergedIntoParent]
    ///  * [mergeAllDescendantsIntoThisNode]
    bool get isPartOfNodeMerging => mergeAllDescendantsIntoThisNode || isMergedIntoParent;
  