Further clarification of directory-files* doc

* doc/lispref/files.texi (Contents of Directories):
Precise description of MATCH-REGEXP of directory-files.  Add
directory-files-no-dot-files-regexp.

* lisp/files.el (directory-files-no-dot-files-regexp): Revert last fix.

* src/dired.c (Fdirectory_files)
(Fdirectory_files_and_attributes): Fix wording in docstring.

doc/lispref/files.texi

@@ -2926,11 +2926,11 @@ absolute file names.  Otherwise, it returns the names relative to
 the specified directory.
 
 If @var{match-regexp} is non-@code{nil}, this function returns only
-those file names that contain a match for that regular expression---the
+those file names whose non-directory part contain a match for that
-other file names are excluded from the list.  On case-insensitive
+regular expression---the other file names are excluded from the list.
-filesystems, the regular expression matching is case-insensitive.
+On case-insensitive filesystems, the regular expression matching is
+case-insensitive.
 
-@c Emacs 19 feature
 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
 the list, so you get the file names in no particular order.  Use this if
 you want the utmost possible speed and don't care what order the files
@@ -3007,6 +3007,19 @@ corresponding argument to @code{file-attributes} (@pxref{Definition
 of file-attributes}).
 @end defun
 
+@defvr Constant directory-files-no-dot-files-regexp
+This regular expression matches any file name except @samp{.} and
+@samp{..}.  More precisely, it matches parts of any nonempty string
+except those two.  It is useful as the @var{match-regexp} argument to
+@code{directory-files} and @code{directory-files-and-attributes}:
+
+@example
+(directory-files "/foo" nil directory-files-no-dot-files-regexp)
+@end example
+
+returns @code{nil}, if directory @samp{/foo} is empty.
+@end defvr
+
 @defun file-expand-wildcards pattern &optional full
 This function expands the wildcard pattern @var{pattern}, returning
 a list of file names that match it.

lisp/files.el

@@ -5787,7 +5787,7 @@ If called interactively, then PARENTS is non-nil."
 
 (defconst directory-files-no-dot-files-regexp
   "[^.]\\|\\.\\.\\."
-  "Regexp matching any non-directory part of a file name except \".\" and \"..\".
+  "Regexp matching any file name except \".\" and \"..\".
 More precisely, it matches parts of any nonempty string except those two.
 It is useful as the regexp argument to `directory-files' and
 `directory-files-and-attributes'.")

src/dired.c

@@ -293,7 +293,7 @@ DEFUN ("directory-files", Fdirectory_files, Sdirectory_files, 1, 4, 0,
 There are three optional arguments:
 If FULL is non-nil, return absolute file names.  Otherwise return names
  that are relative to the specified directory.
-If MATCH is non-nil, mention only file names which non-directory part
+If MATCH is non-nil, mention only file names whose non-directory part
  matches the regexp MATCH.
 If NOSORT is non-nil, the list is not sorted--its order is unpredictable.
  Otherwise, the list returned is sorted with `string-lessp'.
@@ -326,7 +326,7 @@ by `file-attributes'.
 This function accepts four optional arguments:
 If FULL is non-nil, return absolute file names.  Otherwise return names
  that are relative to the specified directory.
-If MATCH is non-nil, mention only file names which non-directory part
+If MATCH is non-nil, mention only file names whose non-directory part
  matches the regexp MATCH.
 If NOSORT is non-nil, the list is not sorted--its order is unpredictable.
  NOSORT is useful if you plan to sort the result yourself.