Whenever the user selects the extension's main menu item from File Manager's menu bar, File Manager sends the FMEVENT_INITMENU message to the extension DLL. An extension can use this message to initialize its menu items. For example, an extension can add check marks, disable items, or gray items during this message.
When the user selects submenus within the extension's menu, File Manager does not send the FMEVENT_INITMENU message. An extension DLL must initialize all items at the same time, including those in submenus.