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+;; Edit Options command for Emacs.
+;; Copyright (C) 1985 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 1, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to
+;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+
+(defun list-options ()
+  "Display a list of Emacs user options, with values and documentation."
+  (interactive)
+  (save-excursion
+    (set-buffer (get-buffer-create "*List Options*"))
+    (Edit-options-mode))
+  (with-output-to-temp-buffer "*List Options*"
+    (let (vars)
+      (mapatoms (function (lambda (sym)
+			    (if (user-variable-p sym)
+				(setq vars (cons sym vars))))))
+      (setq vars (sort vars 'string-lessp))
+      (while vars
+	(let ((sym (car vars)))
+	  (princ ";; ")
+	  (prin1 sym)
+	  (princ ":\n\t")
+	  (prin1 (symbol-value sym))
+	  (terpri)
+	  (princ (substitute-command-keys 
+		  (documentation-property sym 'variable-documentation)))
+	  (princ "\n;;\n"))
+	(setq vars (cdr vars))))))
+
+(defun edit-options ()
+  "Edit a list of Emacs user option values.
+Selects a buffer containing such a list,
+in which there are commands to set the option values.
+Type \\[describe-mode] in that buffer for a list of commands."
+  (interactive)
+  (list-options)
+  (pop-to-buffer "*List Options*"))
+
+(defvar Edit-options-mode-map
+  (let ((map (make-keymap)))
+    (define-key map "s" 'Edit-options-set)
+    (define-key map "x" 'Edit-options-toggle)
+    (define-key map "1" 'Edit-options-t)
+    (define-key map "0" 'Edit-options-nil)
+    (define-key map "p" 'backward-paragraph)
+    (define-key map " " 'forward-paragraph)
+    (define-key map "n" 'forward-paragraph)
+    map)
+  "")
+
+;; Edit Options mode is suitable only for specially formatted data.
+(put 'Edit-options-mode 'mode-class 'special)
+
+(defun Edit-options-mode ()
+  "Major mode for editing Emacs user option settings.
+Special commands are:
+s -- set variable point points at.  New value read using minibuffer.
+x -- toggle variable, t -> nil, nil -> t.
+1 -- set variable to t.
+0 -- set variable to nil.
+Changed values made by these commands take effect immediately.
+
+Each variable description is a paragraph.
+For convenience, the characters p and n move back and forward by paragraphs."
+  (kill-all-local-variables)
+  (set-syntax-table emacs-lisp-mode-syntax-table)
+  (use-local-map Edit-options-mode-map)
+  (make-local-variable 'paragraph-separate)
+  (setq paragraph-separate "[^\^@-\^?]")
+  (make-local-variable 'paragraph-start)
+  (setq paragraph-start "^\t")
+  (setq truncate-lines t)
+  (setq major-mode 'Edit-options-mode)
+  (setq mode-name "Options")
+  (run-hooks 'Edit-options-mode-hook))
+
+(defun Edit-options-set () (interactive)
+  (Edit-options-modify
+   '(lambda (var) (eval-minibuffer (concat "New " (symbol-name var) ": ")))))
+
+(defun Edit-options-toggle () (interactive)
+  (Edit-options-modify '(lambda (var) (not (symbol-value var)))))
+
+(defun Edit-options-t () (interactive)
+  (Edit-options-modify '(lambda (var) t)))
+
+(defun Edit-options-nil () (interactive)
+  (Edit-options-modify '(lambda (var) nil)))
+
+(defun Edit-options-modify (modfun)
+  (save-excursion
+   (let (var pos)
+     (re-search-backward "^;; \\|\\`")
+     (forward-char 3)
+     (setq pos (point))
+     (save-restriction
+       (narrow-to-region pos (progn (end-of-line) (1- (point))))
+       (goto-char pos)
+       (setq var (read (current-buffer))))
+     (goto-char pos)
+     (forward-line 1)
+     (forward-char 1)
+     (save-excursion
+       (set var (funcall modfun var)))
+     (kill-sexp 1)
+     (prin1 (symbol-value var) (current-buffer)))))
+