Function: recentf-mode

Toggle "Open Recent" menu (Recentf mode).
With a prefix argument ARG, enable Recentf mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
Recentf mode if ARG is omitted or nil.

When Recentf mode is enabled, a "Open Recent" submenu is
displayed in the "File" menu, containing a list of files that
were operated on recently. (fn &optional ARG)

Variable: recentf-mode

Non-nil if Recentf mode is enabled.
See the command `recentf-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `recentf-mode'.