(defun dired-current-directory (&optional localp)
"Return the name of the subdirectory to which this line belongs.
This returns a string with trailing slash, like `default-directory'.
-Optional argument means return a file name relative to `default-directory'."
+Optional argument means return a file name relative to `default-directory',
+in which case the value could be an empty string if `default-directory'
+is the directory where the file on this line resides."
(let ((here (point))
(alist (or dired-subdir-alist
;; probably because called in a non-dired buffer