-Toggle use of Ibuffer's auto-update facility.
-With numeric ARG, enable auto-update if and only if ARG is positive.
+Toggle use of Ibuffer's auto-update facility (Ibuffer Auto mode).
+With a prefix argument ARG, enable Ibuffer Auto mode if ARG is
+positive, and disable it otherwise. If called from Lisp, enable
+the mode if ARG is omitted or nil.