File Manager sends, first, the FMEVENT_LOAD message to the FMExtensionProc function. The lParam parameter that accompanies the FMEVENT_LOAD message points to an FMS_LOAD structure that File Manager uses to obtain information about the extension-supplied menu, including the menu name and menu handle. For detailed information about the FMS_LOAD structure, see the Microsoft Windows Programmer's Reference, Volume 3.
File Manager also uses the FMS_LOAD structure to pass the menu-item delta value to the extension. To avoid conflicts with its own menu-item identifiers, File Manager renumbers the menu-item identifiers in an extension-supplied menu by adding the delta value to each identifier. If an extension DLL needs to modify its menu after File Manager has loaded it, it must use the delta value. For example, to delete a menu item, the extension DLL finds the sum of the delta value and the menu item's identifier and then passes the sum as the idItem parameter to the DeleteMenu function.