- "Turn directory tracking on and off in a shell buffer.
-The `dirtrack' package provides an alternative implementation of this
-feature - see the function `dirtrack-mode'."
+ "Toggle directory tracking in this shell buffer (Shell Dirtrack mode).
+With a prefix argument ARG, enable Shell Dirtrack mode if ARG is
+positive, and disable it otherwise. If called from Lisp, enable
+the mode if ARG is omitted or nil.
+
+The `dirtrack' package provides an alternative implementation of
+this feature; see the function `dirtrack-mode'."