- "Toggle automatic file compression and uncompression.
-With prefix argument ARG, turn auto compression on if positive, else off.
-Return the new status of auto compression (non-nil means on)."
+ "Toggle Auto Compression mode.
+With a prefix argument ARG, enable Auto Compression mode if ARG
+is positive, and disable it otherwise. If called from Lisp,
+enable the mode if ARG is omitted or nil.
+
+Auto Compression mode is a global minor mode. When enabled,
+compressed files are automatically uncompressed for reading, and
+compressed when writing."