buffer-face-mode is an interactive autoloaded compiled Lisp function in `face-remap.el'.

(buffer-face-mode &optional ARG)

Minor mode for a buffer-specific default face.
With a prefix argument ARG, enable the mode if ARG is positive,
and disable it otherwise. If called from Lisp, enable the mode
if ARG is omitted or nil. When enabled, the face specified by the
variable `buffer-face-mode-face' is used to display the buffer text.