Use "#+attr_org: :radio" before lists to enable radio buttons

* doc/org-manual.org (Checkboxes): Document the use of
"#+attr_org".

* lisp/org.el (org-ctrl-c-ctrl-c): When the list at point is
preceded by "#+attr_org: :radio" use `org-toggle-radio-button'
instead of `org-toggle-checkbox'.

* lisp/org-list.el (org-at-radio-list-p): New defsubst.
(org-toggle-checkbox): Use it.

* etc/ORG-NEWS: Document the use of "#+attr_org".

doc/org-manual.org

@@ -4539,12 +4539,13 @@ The following commands work with checkboxes:
   Toggle checkbox status by using the checkbox of the item at point as
   a radio button: when turned on, all other checkboxes on the same
   level will be turned off.  With a universal prefix argument, toggle
-  the presence of the checkbox.  With double prefix argument, set it
+  the presence of the checkbox.  With a double prefix argument, set it
   to =[-]=.
 
   #+findex: org-list-checkbox-radio-mode
-  {{{kdb(C-c C-c)}}} can be told to consider checkboxes as radio buttons
-  by calling {{{kbd(M-x org-list-checkbox-radio-mode)}}}, as minor mode.
+  {{{kdb(C-c C-c)}}} can be told to consider checkboxes as radio buttons by
+  setting =#+ATTR_ORG: :radio= right before the list or by calling
+  {{{kbd(M-x org-list-checkbox-radio-mode)}}} to activate this minor mode.
 
 - {{{kbd(M-S-RET)}}} (~org-insert-todo-heading~) ::
 

etc/ORG-NEWS

@@ -54,6 +54,9 @@ If you want to occasionally toggle a checkbox as a radio button
 without turning this minor mode on, you can use =<C-c C-x C-r>= to
 call ~org-toggle-radio-button~.
 
+You can also add =#+ATTR_ORG: :radio= right before the list to tell
+Org to use radio buttons for this list only.
+
 *** Looping agenda commands over headlines
 
 ~org-agenda-loop-over-headlines-in-active-region~ allows you to loop

lisp/org-list.el

@@ -2337,6 +2337,16 @@ is an integer, 0 means `-', 1 means `+' etc.  If WHICH is
       (org-list-struct-apply-struct struct old-struct)
       (org-update-checkbox-count-maybe))))
 
+(defsubst org-at-radio-list-p ()
+  "Is point in a list with radio buttons?"
+  (let (attr)
+    (save-excursion
+      (org-at-item-p)
+      (goto-char (caar (org-list-struct)))
+      (org-backward-element)
+      (setq attr (car (org-element-property :attr_org (org-element-at-point))))
+      (when attr (string-match-p ":radio" attr)))))
+
 (defun org-toggle-checkbox (&optional toggle-presence)
   "Toggle the checkbox in the current line.
 
@@ -2351,6 +2361,8 @@ If point is on a headline, apply this to all checkbox items in
 the text below the heading, taking as reference the first item in
 subtree, ignoring planning line and any drawer following it."
   (interactive "P")
+  (if (org-at-radio-list-p)
+      (org-toggle-radio-button toggle-presence)
     (save-excursion
       (let* (singlep
 	     block-item
@@ -2436,7 +2448,7 @@ subtree, ignoring planning line and any drawer following it."
 	    (goto-char bottom)
 	    (move-marker bottom nil)
 	    (org-list-struct-apply-struct struct struct-copy)))
-      (move-marker lim-down nil)))
+	(move-marker lim-down nil))))
   (org-update-checkbox-count-maybe))
 
 (defun org-reset-checkbox-state-subtree ()

lisp/org.el

@@ -17171,6 +17171,7 @@ This command does many different things, depending on context:
 			  src-block statistics-cookie table table-cell table-row
 			  timestamp)
 	     t))
+	   (radio-list-p (org-at-radio-list-p))
 	   (type (org-element-type context)))
       ;; For convenience: at the first line of a paragraph on the same
       ;; line as an item, apply function on that item instead.
@@ -17217,8 +17218,9 @@ This command does many different things, depending on context:
 	 ;; unconditionally, whereas `C-u' will toggle its presence.
 	 ;; Without a universal argument, if the item has a checkbox,
 	 ;; toggle it.  Otherwise repair the list.
-	 (if (and (boundp org-list-checkbox-radio-mode)
-		  org-list-checkbox-radio-mode)
+	 (if (or radio-list-p
+		 (and (boundp org-list-checkbox-radio-mode)
+		      org-list-checkbox-radio-mode))
 	     (org-toggle-radio-button arg)
 	   (let* ((box (org-element-property :checkbox context))
 		  (struct (org-element-property :structure context))
@@ -17259,8 +17261,9 @@ This command does many different things, depending on context:
 	 ;; will toggle their presence according to the state of the
 	 ;; first item in the list.  Without an argument, repair the
 	 ;; list.
-	 (if (and (boundp org-list-checkbox-radio-mode)
-		  org-list-checkbox-radio-mode)
+	 (if (or radio-list-p
+		 (and (boundp org-list-checkbox-radio-mode)
+		      org-list-checkbox-radio-mode))
 	     (org-toggle-radio-button arg)
 	   (let* ((begin (org-element-property :contents-begin context))
 		  (struct (org-element-property :structure context))