+ ;; a-r-tail-pos stores the size of the file at the time of the
+ ;; last revert. After this package loads, it adds a
+ ;; find-file-hook to set this variable every time a file is
+ ;; loaded. If the package is loaded only _after_ visiting the
+ ;; file to be reverted, then we have no idea what the value of
+ ;; a-r-tail-pos should have been when the file was visited. If
+ ;; the file has changed on disk in the meantime, all we can do
+ ;; is offer to revert the whole thing. If you choose not to
+ ;; revert, then you might miss some output then happened
+ ;; between visiting the file and activating a-r-t-mode.
+ (and (zerop auto-revert-tail-pos)
+ (not (verify-visited-file-modtime (current-buffer)))
+ (y-or-n-p "File changed on disk, content may be missing. \
+Perform a full revert? ")
+ ;; Use this (not just revert-buffer) for point-preservation.
+ (auto-revert-handler))