This attribute is set to a pointer to the struct MenuItem of
the item object when the item is selected. By setting up
notification on this attribute with MUIV_EveryTime, you can
react on menu actions and query the MenuItems flags
immediately.
Note that menu reactions are also possible any
maybe a bit easier with MUIA_Application_ReturnID,
MUIA_Application_MenuAction and MUIA_Window_MenuAction.