on-menu-char in frame%

If the frame has a menu bar with keyboard shortcuts, and if the key event includes a Control, Alt, Option, Meta, Command, Shift, or Function key, then on-menu-char attempts to match the given event to a menu item. If a match is found, #t is returned, otherwise #f is returned.

When the match corresponds to a complete shortcut combination, the menu item's callback is called (before on-menu-char returns).

If the event does not correspond to a complete shortcut combination, the event may be handled anyway if it corresponds to a mnemonic in the menu bar (i.e., an underlined letter in a menu's title, which is installed by including an ampersand in the menu's label). If a mnemonic match is found, the keyboard focus is moved to the menu bar (selecting the menu with the mnemonic), and #t is returned.