+ virtual std::string state_id() const = 0;
+ /* for now, we always return properties in string form.
+ */
+ std::string gui_property (const std::string& property_name) const;
+
+ template<typename T> void set_gui_property (const std::string& property_name, const T& value) {
+ gui_object_state().set_property<T> (state_id(), property_name, value);
+ }
+
+ bool marked_for_display () const;
+ virtual bool set_marked_for_display (bool);
+
+ static GUIObjectState& gui_object_state();
+