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From: tom@uw-warp.UUCP (F. Thomas May)
Newsgroups: comp.emacs
Subject: Re: gnuemacs quesion: what does (put 'xxxx-mode 'mode-class 'special) do?
Message-ID: <269@uw-warp.UUCP>
Date: Sat, 5-Sep-87 16:01:05 EDT
Article-I.D.: uw-warp.269
Posted: Sat Sep  5 16:01:05 1987
Date-Received: Sun, 6-Sep-87 09:52:11 EDT
References: <740@hplabsz.HPL.HP.COM>
Organization: The Warp, Seattle, WA
Lines: 32
In-reply-to: mayer@hplabsz.HPL.HP.COM's message of 31 Aug 87 01:12:57 GMT


In article <740@hplabsz.HPL.HP.COM> mayer@hplabsz.HPL.HP.COM (Niels Mayer)
writes:

   a few examples of where the mode-class property is used:
     blackbox.el   :: (put 'blackbox-mode 'mode-class 'special)
     buff-menu.el  :: (put 'buffer-menu-mode 'mode-class 'special)
     dired.el      :: (put 'dired-mode 'mode-class 'special)
     ebuff-menu.el :: (put 'Electric-buffer-menu-mode 'mode-class 'special)

   Can someone explain why this is done?

This is not at all obvious, but if you look at the documentation for
the variable default-major-mode it says:

*Major mode for new buffers.  Defaults to fundamental-mode.
nil here means use current buffer's major mode.

What it should say is:

*Major mode for new buffers.  Defaults to fundamental-mode.
nil here means use current buffer's major mode, unless the mode-class
property of the current buffer's major mode is non-nil,
in which case use fundamental-mode.

This just keeps newly created buffers from being in modes, such as
blackbox-mode, that are useful only for specially formatted data or
for doing special things.  The result is that if you C-x b to a new
buffer in the middle of a blackbox game to write yourself a note or
something, the buffer ends up in a mode you can use for editing.
-- 
Tom May
uw-nsr!uw-warp!tom@beaver.cs.washington.edu
uw-beaver!uw-nsr!uw-warp!tom