+ -- ** -- P R I V A T E D A T A ---------------------------------------------
+ */
+
+private:
+
+ sigc::signal<void> signal_undo_tree_changed_;
+
+ /*
+ -- ** -- S I G N A L I N T E R F A C E S -----------------------------------
+ */
+
+public:
+
+ sigc::signal<void>& signal_undo_tree_changed() { return signal_undo_tree_changed_; }
+
+ /*