Re: Undocumented menu feature?

[Sergey Organov <sorganov@gmail.com>]

Jan Djärv <jan.h.d@swipnet.se> writes:

> Hi.
>
> 2 okt 2014 kl. 16:34 skrev Sergey Organov <sorganov@gmail.com>:
>
>> Hello,
>> 
>> I've asked this in help-gnu-emacs, but nobody seems to have a clue
>> there. Hopefully some developer(s) knwow.
>> 
>> Here is the reference:
>> 
>> http://lists.gnu.org/archive/html/help-gnu-emacs/2014-10/msg00007.html
>> 
>> And here is my original question:
>> 
>> I suddenly found that my emacs (GNU Emacs 23.2.1, running on
>> Debian/Gnome) is capable of "detaching" some sub-menus and putting them
>> into separate frames. For example, if I click "File" in the main menu,
>> submenu appears containing dashed line at the top, and if I click on
>> that dashed line, entire "File" submenu appears in a separate frame.
>> 
>> I can't find anything about the feature by googling for it. Could somebody
>> please point me to relevant documentation?
>
> We don't have Emacs specific documentation for this, it is a standard
> Gtk+ feature. About to be deprecated in Gtk+ I think.

Thanks, but first I don't see it in any other application but Emacs, and
second it looks to be somehow controlled from within Emacs:

Some of Emacs submenus do have it, and some don't. For example, in
"Options", the "Line Wrapping in this Buffer" submenu has the dashed
line, while neither "Mule (Multilingual Environment)" nor "Customize
Emacs" have one.

I can't figure any template, as some submenus of non-detachable menus
could be detachable, and vice versa. Moreover, ["Tools" "Spell
Checking"] has this active dashed line right in the middle (between 
"Complete Word Fragment" and "Complete Word"), not at the top.

The latter makes one think it's some special kind of separator, but I
fail to see something relevant in "22.17.1.3 Menu Separators."

How do I control it from Emacs?

-- 
Sergey.