parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
(or @dfn{file name within the directory}). Either part may be empty.
Concatenating these two parts reproduces the original file name.
+@footnote{Emacs follows the GNU convention to use the term @emph{file name}
+instead of the term @emph{pathname}. We use the term @emph{path} only for
+search paths, which are lists of directory names.}
On most systems, the directory part is everything up to and including
the last slash (backslash is also allowed in input on MS-DOS or