Merge from origin/emacs-27

f60eb988f6 Fix typos and omissions for (elisp)Button Buffer Commands
876b95bf90 Teach Rmail about NBSP in "Re:"

# Conflicts:
#	lisp/mail/rmail.el

diff --cc doc/lispref/display.texi
Simple merge

diff --cc lisp/mail/rmail.el
index 2bd3ffa29106394338f4a2d9e271e44ae4e4843f,86154f2a61fb00e96d6b804d080915e0b95a8b85..c7960f85043bc4d45ba912ba2556a07beac349fd
--- 1/lisp/mail/rmail.el
--- 2/lisp/mail/rmail.el
+++ b/lisp/mail/rmail.el
@@@ -548,10 -582,7 +548,10 @@@ Examples
  ;; This pattern should catch all the common variants.
  ;; rms: I deleted the change to delete tags in square brackets
  ;; because they mess up RT tags.
 -(defvar rmail-reply-regexp "\\`\\(Re\\(([0-9]+)\\|\\[[0-9]+\\]\\|\\^[0-9]+\\)?\u00a0*: *\\)*"
 +(defvar rmail-reply-regexp
 +  (concat "\\`\\("
 +          rmail-re-abbrevs
-           "\\(([0-9]+)\\|\\[[0-9]+\\]\\|\\^[0-9]+\\)?[:：] *\\)*")
++          "\\(([0-9]+)\\|\\[[0-9]+\\]\\|\\^[0-9]+\\)?\u00a0*[:：] *\\)*")
    "Regexp to delete from Subject line before inserting `rmail-reply-prefix'.")
  
  (defcustom rmail-display-summary nil
@@@ -3356,7 -3398,8 +3356,7 @@@ whitespace, replacing whitespace runs w
  removing prefixes such as Re:, Fwd: and so on and mailing list
  tags such as [tag]."
    (let ((subject (or (rmail-get-header "Subject" msgnum) ""))
-       (regexp "\\`[ \t\n]*\\(\\(\\w\\{1,4\\}[:：]\\|\\[[^]]+]\\)[ \t\n]+\\)*"))
 -      (regexp
 -         "\\`[ \t\n]*\\(\\(\\w\\{1,3\\}\u00a0*:\\|\\[[^]]+]\\)[ \t\n]+\\)*"))
++      (regexp "\\`[ \t\n]*\\(\\(\\w\\{1,4\\}\u00a0*[:：]\\|\\[[^]]+]\\)[ \t\n]+\\)*"))
      (setq subject (rfc2047-decode-string subject))
      (setq subject (replace-regexp-in-string regexp "" subject))
      (replace-regexp-in-string "[ \t\n]+" " " subject)))