To modify the system menu.
winio@('%sm[menu_spec]', . . .)
Grave accent (`) - used to replace rather than add to the existing
Question mark (?) - All the strings are placed in order at the end of the format
description, one for each and every menu item that has a call-back function.
If you want the percentage character % to appear in the text of a menu
item then you must put %% in the code.
%mn - Menu, %pm - Popup Menu