Improve regexp advice again, and unchain ranges

* doc/lispref/searching.texi (Regexp Special):
Mention char classes earlier, in a more-logical place.
Advise sticking to ASCII letters and digits in ranges.
Reword negative advice to make it clearer that it’s negative.
* lisp/files.el (make-auto-save-file-name):
* lisp/gnus/message.el (message-mailer-swallows-blank-line):
* lisp/gnus/nndoc.el (nndoc-lanl-gov-announce-type-p)
(nndoc-generate-lanl-gov-head):
* lisp/org/org-eshell.el (org-eshell-open):
* lisp/org/org.el (org-deadline-time-hour-regexp)
(org-scheduled-time-hour-regexp):
* lisp/progmodes/bat-mode.el (bat-font-lock-keywords):
* lisp/progmodes/bug-reference.el (bug-reference-bug-regexp):
* lisp/textmodes/less-css-mode.el (less-css-font-lock-keywords):
* lisp/vc/vc-cvs.el (vc-cvs-valid-symbolic-tag-name-p):
* lisp/vc/vc-svn.el (vc-svn-valid-symbolic-tag-name-p):
Avoid attempts to chain ranges, as this can be confusing.
For example, instead of [0-9-_.], use [0-9_.-].

11 files changed, 45 insertions, 33 deletions

diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
index 72ee9233a3c..8775254dd07 100644
--- a/doc/lispref/searching.texi
+++ b/doc/lispref/searching.texi
@@ -395,9 +395,18 @@ or @samp{$}, @samp{%} or period.  However, the ending character of one
 range should not be the starting point of another one; for example,
 @samp{[a-m-z]} should be avoided.
 
+A character alternative can also specify named character classes
+(@pxref{Char Classes}).  This is a POSIX feature.  For example,
+@samp{[[:ascii:]]} matches any @acronym{ASCII} character.
+Using a character class is equivalent to mentioning each of the
+characters in that class; but the latter is not feasible in practice,
+since some classes include thousands of different characters.
+A character class should not appear as the lower or upper bound
+of a range.
+
 The usual regexp special characters are not special inside a
 character alternative.  A completely different set of characters is
-special inside character alternatives: @samp{]}, @samp{-} and @samp{^}.
+special: @samp{]}, @samp{-} and @samp{^}.
 To include @samp{]} in a character alternative, put it at the
 beginning.  To include @samp{^}, put it anywhere but at the beginning.
 To include @samp{-}, put it at the end.  Thus, @samp{[]^-]} matches
@@ -430,33 +439,36 @@ matches only @samp{/} rather than the likely-intended four characters.
 @end enumerate
 
 Some kinds of character alternatives are not the best style even
-though they are standardized by POSIX and are portable.  They include:
+though they have a well-defined meaning in Emacs.  They include:
 
 @enumerate
 @item
-A character alternative can include duplicates.  For example,
-@samp{[XYa-yYb-zX]} is less clear than @samp{[XYa-z]}.
+Although a range's bound can be almost any character, it is better
+style to stay within natural sequences of ASCII letters and digits
+because most people have not memorized character code tables.
+For example, @samp{[.-9]} is less clear than @samp{[./0-9]},
+and @samp{[`-~]} is less clear than @samp{[`a-z@{|@}~]}.
+Unicode character escapes can help here; for example, for most programmers
+@samp{[ก-ฺ฿-๛]} is less clear than @samp{[\u0E01-\u0E3A\u0E3F-\u0E5B]}.
 
 @item
-A range can denote just one, two, or three characters.  For example,
-@samp{[(-(]} is less clear than @samp{[(]}, @samp{[*-+]} is less clear
-than @samp{[*+]}, and @samp{[*-,]} is less clear than @samp{[*+,]}.
+Although a character alternative can include duplicates, it is better
+style to avoid them.  For example, @samp{[XYa-yYb-zX]} is less clear
+than @samp{[XYa-z]}.
 
 @item
-A @samp{-} also appear at the beginning of a character alternative, or
-as the upper bound of a range.  For example, although @samp{[-a-z]} is
-valid, @samp{[a-z-]} is better style; and although @samp{[!--/]} is
-valid, @samp{[!-,/-]} is clearer.
-@end enumerate
+Although a range can denote just one, two, or three characters, it
+is simpler to list the characters.  For example,
+@samp{[a-a0]} is less clear than @samp{[a0]}, @samp{[i-j]} is less clear
+than @samp{[ij]}, and @samp{[i-k]} is less clear than @samp{[ijk]}.
 
-A character alternative can also specify named character classes
-(@pxref{Char Classes}).  This is a POSIX feature.  For example,
-@samp{[[:ascii:]]} matches any @acronym{ASCII} character.
-Using a character class is equivalent to mentioning each of the
-characters in that class; but the latter is not feasible in practice,
-since some classes include thousands of different characters.
-A character class should not appear as the lower or upper bound
-of a range.
+@item
+Although a @samp{-} can appear at the beginning of a character
+alternative or as the upper bound of a range, it is better style to
+put @samp{-} by itself at the end of a character alternative.  For
+example, although @samp{[-a-z]} is valid, @samp{[a-z-]} is better
+style; and although @samp{[*--]} is valid, @samp{[*+,-]} is clearer.
+@end enumerate
 
 @item @samp{[^ @dots{} ]}
 @cindex @samp{^} in regexp
diff --git a/lisp/files.el b/lisp/files.el
index 77a194b085d..1dae57593a0 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -6316,7 +6316,7 @@ See also `auto-save-file-name-p'."
       ;; We do this on all platforms, because even if we are not
       ;; running on DOS/Windows, the current directory may be on a
       ;; mounted VFAT filesystem, such as a USB memory stick.
-      (while (string-match "[^A-Za-z0-9-_.~#+]" buffer-name limit)
+      (while (string-match "[^A-Za-z0-9_.~#+-]" buffer-name limit)
         (let* ((character (aref buffer-name (match-beginning 0)))
                (replacement
                 ;; For multibyte characters, this will produce more than
diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index dae4b0dced6..c8b6f0ee685 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -1288,7 +1288,7 @@ called and its result is inserted."
       ;; According to RFC 822 and its successors, the field name must
       ;; consist of printable US-ASCII characters other than colon,
       ;; i.e., decimal 33-56 and 59-126.
-      '(looking-at "[ \t]\\|[][!\"#$%&'()*+,-./0-9;<=>?@A-Z\\^_`a-z{|}~]+:"))
+      '(looking-at "[ \t]\\|[][!\"#$%&'()*+,./0-9;<=>?@A-Z\\^_`a-z{|}~-]+:"))
   "Set this non-nil if the system's mailer runs the header and body together.
 \(This problem exists on Sunos 4 when sendmail is run in remote mode.)
 The value should be an expression to test whether the problem will
diff --git a/lisp/gnus/nndoc.el b/lisp/gnus/nndoc.el
index 8f1217b1275..532ba11fa09 100644
--- a/lisp/gnus/nndoc.el
+++ b/lisp/gnus/nndoc.el
@@ -701,7 +701,7 @@ from the document.")
 
 (defun nndoc-lanl-gov-announce-type-p ()
   (when (let ((case-fold-search nil))
-          (re-search-forward "^\\\\\\\\\n\\(Paper\\( (\\*cross-listing\\*)\\)?: [a-zA-Z-\\.]+/[0-9]+\\|arXiv:\\)" nil t))
+          (re-search-forward "^\\\\\\\\\n\\(Paper\\( (\\*cross-listing\\*)\\)?: [a-zA-Z\\.-]+/[0-9]+\\|arXiv:\\)" nil t))
     t))
 
 (defun nndoc-transform-lanl-gov-announce (article)
@@ -732,7 +732,7 @@ from the document.")
       (save-restriction
         (narrow-to-region (car entry) (nth 1 entry))
         (goto-char (point-min))
-        (when (looking-at "^\\(Paper.*: \\|arXiv:\\)\\([0-9a-zA-Z-\\./]+\\)")
+        (when (looking-at "^\\(Paper.*: \\|arXiv:\\)\\([0-9a-zA-Z\\./-]+\\)")
           (setq subject (concat " (" (match-string 2) ")"))
           (when (re-search-forward "^From: \\(.*\\)" nil t)
             (setq from (concat "<"
diff --git a/lisp/org/org-eshell.el b/lisp/org/org-eshell.el
index bb27d92e12d..2251a1b892f 100644
--- a/lisp/org/org-eshell.el
+++ b/lisp/org/org-eshell.el
@@ -37,7 +37,7 @@
    eshell buffer) or a command line prefixed by a buffer name
    followed by a colon."
   (let* ((buffer-and-command
-          (if (string-match "\\([A-Za-z0-9-+*]+\\):\\(.*\\)" link)
+          (if (string-match "\\([A-Za-z0-9+*-]+\\):\\(.*\\)" link)
               (list (match-string 1 link)
                     (match-string 2 link))
             (list eshell-buffer-name link)))
diff --git a/lisp/org/org.el b/lisp/org/org.el
index bf7e305b7a0..ce6dd24a83b 100644
--- a/lisp/org/org.el
+++ b/lisp/org/org.el
@@ -430,7 +430,7 @@ Matched keyword is in group 1.")
 
 (defconst org-deadline-time-hour-regexp
   (concat "\\<" org-deadline-string
-          " *<\\([^>]+[0-9]\\{1,2\\}:[0-9]\\{2\\}[0-9-+:hdwmy \t.]*\\)>")
+          " *<\\([^>]+[0-9]\\{1,2\\}:[0-9]\\{2\\}[0-9+:hdwmy \t.-]*\\)>")
   "Matches the DEADLINE keyword together with a time-and-hour stamp.")
 
 (defconst org-deadline-line-regexp
@@ -446,7 +446,7 @@ Matched keyword is in group 1.")
 
 (defconst org-scheduled-time-hour-regexp
   (concat "\\<" org-scheduled-string
-          " *<\\([^>]+[0-9]\\{1,2\\}:[0-9]\\{2\\}[0-9-+:hdwmy \t.]*\\)>")
+          " *<\\([^>]+[0-9]\\{1,2\\}:[0-9]\\{2\\}[0-9+:hdwmy \t.-]*\\)>")
   "Matches the SCHEDULED keyword together with a time-and-hour stamp.")
 
 (defconst org-closed-time-regexp
diff --git a/lisp/progmodes/bat-mode.el b/lisp/progmodes/bat-mode.el
index 6c85ff99053..a8b002be59b 100644
--- a/lisp/progmodes/bat-mode.el
+++ b/lisp/progmodes/bat-mode.el
@@ -78,7 +78,7 @@
              "goto" "gtr" "if" "in" "leq" "lss" "neq" "not" "start"))
           (UNIX
            '("bash" "cat" "cp" "fgrep" "grep" "ls" "sed" "sh" "mv" "rm")))
-      `(("\\_<\\(call\\|goto\\)\\_>[ \t]+%?\\([A-Za-z0-9-_\\:.]+\\)%?"
+      `(("\\_<\\(call\\|goto\\)\\_>[ \t]+%?\\([A-Za-z0-9_\\:.-]+\\)%?"
          (2 font-lock-constant-face t))
         ("^:[^:].*"
          . 'bat-label-face)
diff --git a/lisp/progmodes/bug-reference.el b/lisp/progmodes/bug-reference.el
index 8baf74854f6..759db1f5686 100644
--- a/lisp/progmodes/bug-reference.el
+++ b/lisp/progmodes/bug-reference.el
@@ -69,7 +69,7 @@ so that it is considered safe, see `enable-local-variables'.")
                 (get s 'bug-reference-url-format)))))
 
 (defcustom bug-reference-bug-regexp
-  "\\([Bb]ug ?#?\\|[Pp]atch ?#\\|RFE ?#\\|PR [a-z-+]+/\\)\\([0-9]+\\(?:#[0-9]+\\)?\\)"
+  "\\([Bb]ug ?#?\\|[Pp]atch ?#\\|RFE ?#\\|PR [a-z+-]+/\\)\\([0-9]+\\(?:#[0-9]+\\)?\\)"
   "Regular expression matching bug references.
 The second subexpression should match the bug reference (usually a number)."
   :type 'string
diff --git a/lisp/textmodes/less-css-mode.el b/lisp/textmodes/less-css-mode.el
index b4c7f28985d..4077789eb12 100644
--- a/lisp/textmodes/less-css-mode.el
+++ b/lisp/textmodes/less-css-mode.el
@@ -194,10 +194,10 @@ directory by default."
 ;; - custom faces.
 (defconst less-css-font-lock-keywords
   '(;; Variables
-    ("@[a-z_-][a-z-_0-9]*" . font-lock-variable-name-face)
+    ("@[a-z_-][a-z_0-9-]*" . font-lock-variable-name-face)
     ("&" . font-lock-preprocessor-face)
     ;; Mixins
-    ("\\(?:[ \t{;]\\|^\\)\\(\\.[a-z_-][a-z-_0-9]*\\)[ \t]*;" .
+    ("\\(?:[ \t{;]\\|^\\)\\(\\.[a-z_-][a-z_0-9-]*\\)[ \t]*;" .
      (1 font-lock-keyword-face))))
 
 (defvar less-css-mode-syntax-table
diff --git a/lisp/vc/vc-cvs.el b/lisp/vc/vc-cvs.el
index 3bbd0ed49b1..626e190c1e8 100644
--- a/lisp/vc/vc-cvs.el
+++ b/lisp/vc/vc-cvs.el
@@ -1087,7 +1087,7 @@ CVS/Entries should only be accessed through this function."
   ;; an uppercase or lowercase letter and can contain uppercase and
   ;; lowercase letters, digits, `-', and `_'.
   (and (string-match "^[a-zA-Z]" tag)
-       (not (string-match "[^a-z0-9A-Z-_]" tag))))
+       (not (string-match "[^a-z0-9A-Z_-]" tag))))
 
 (defun vc-cvs-valid-revision-number-p (tag)
   "Return non-nil if TAG is a valid revision number."
diff --git a/lisp/vc/vc-svn.el b/lisp/vc/vc-svn.el
index 618f03eedc5..3c50c8fff64 100644
--- a/lisp/vc/vc-svn.el
+++ b/lisp/vc/vc-svn.el
@@ -759,7 +759,7 @@ Set file properties accordingly.  If FILENAME is non-nil, return its status."
   ;; an uppercase or lowercase letter and can contain uppercase and
   ;; lowercase letters, digits, `-', and `_'.
   (and (string-match "^[a-zA-Z]" tag)
-       (not (string-match "[^a-z0-9A-Z-_]" tag))))
+       (not (string-match "[^a-z0-9A-Z_-]" tag))))
 
 (defun vc-svn-valid-revision-number-p (tag)
   "Return non-nil if TAG is a valid revision number."