Introduce an :interactive keyword for `defined-derived-mode'

* doc/lispref/modes.texi (Derived Modes): Document it.
* lisp/emacs-lisp/derived.el (define-derived-mode): Introduce a
new :interactive keyword.

doc/lispref/modes.texi

@@ -861,6 +861,13 @@ abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table}
 if @var{parent} is @code{nil}.  (Again, a @code{nil} value is
 @emph{not} equivalent to not specifying this keyword.)
 
+@item :interactive
+Modes are interactive commands by default.  If you specify a
+@code{nil} value, the mode defined here won't be interactive.  This is
+useful for modes that are never meant to be activated by users
+manually, but are only supposed to be used in some specially-formatted
+buffer.
+
 @item :group
 If this is specified, the value should be the customization group for
 this mode.  (Not all major modes have one.)  The command

etc/NEWS

@@ -2271,6 +2271,12 @@ back in Emacs 23.1.  The affected functions are: 'make-obsolete',
 This permanently buffer-local variable holds a list of currently
 enabled minor modes in the current buffer (as a list of symbols).
 
++++
+** 'defined-derived-mode' now takes an :interactive argument.
+This can be used to control whether the defined mode is a command
+or not, and is useful when defining commands that aren't meant to be
+used by users directly.
+
 ** The 'values' variable is now obsolete.
 
 ---

lisp/emacs-lisp/derived.el

@@ -141,6 +141,9 @@ KEYWORD-ARGS:
            :after-hook FORM
                    A single lisp form which is evaluated after the mode
                    hooks have been run.  It should not be quoted.
+           :interactive BOOLEAN
+                   Whether the derived mode should be `interactive' or not.
+                   The default is t.
 
 BODY:      forms to execute just before running the
            hooks for the new mode.  Do not use `interactive' here.
@@ -194,6 +197,7 @@ See Info node `(elisp)Derived Modes' for more details.
 	(declare-syntax t)
 	(hook (derived-mode-hook-name child))
 	(group nil)
+        (interactive t)
         (after-hook nil))
 
     ;; Process the keyword args.
@@ -203,6 +207,7 @@ See Info node `(elisp)Derived Modes' for more details.
 	(:abbrev-table (setq abbrev (pop body)) (setq declare-abbrev nil))
 	(:syntax-table (setq syntax (pop body)) (setq declare-syntax nil))
         (:after-hook (setq after-hook (pop body)))
+        (:interactive (setq interactive (pop body)))
 	(_ (pop body))))
 
     (setq docstring (derived-mode-make-docstring
@@ -246,7 +251,7 @@ No problems result if this variable is not bound.
 
        (defun ,child ()
 	 ,docstring
-	 (interactive)
+	 ,(and interactive '(interactive))
 					; Run the parent.
 	 (delay-mode-hooks