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From: mayer@hplabsz.UUCP
Newsgroups: comp.emacs
Subject: gnuemacs quesion: what does (put 'xxxx-mode 'mode-class 'special) do?
Message-ID: <740@hplabsz.HPL.HP.COM>
Date: Sun, 30-Aug-87 21:12:57 EDT
Article-I.D.: hplabsz.740
Posted: Sun Aug 30 21:12:57 1987
Date-Received: Tue, 1-Sep-87 00:43:16 EDT
Reply-To: mayer@hplabsz.UUCP (Niels Mayer)
Organization: Hewlett-Packard Laboratories
Lines: 45


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?


Oh yeah, and while I've got your attention let me ask another question:
what is it about the buffers created by shell-command, dired, etc. that allows
kill-buffer to delete the buffer without querying the user with
"Buffer xyzzy modified; kill anyway?". If one evals buffer-modified-p
in that buffer, it will return 't', yet kill-buffer rightly kills these
buffers without asking.

In buffer.c, buffer-modified-p does
	  bf_cur->text.modified = bf_modified;
	  return buf->save_modified < buf->text.modified ? Qt : Qnil;
to return 't' or 'nil' depending on whether the buffer has been modified.

kill-buffer does
	  /* Make sure b->text.modified is correct
	     even if buffer is selected now.  */
	  bf_cur->text.modified = bf_modified;
	
	  if (INTERACTIVE && !NULL (b->filename)
	      && b->text.modified > b->save_modified)
	    {
	      tem = Fyes_or_no_p (format1 ("Buffer %s modified; kill anyway? ",
					   XSTRING (b->name)->data));
	      if (NULL (tem))
		return Qnil;
	    }
in order to query the user about killing a modified buffer.



-- Niels Mayer
   Hewlett-Packard Laboratories.


PS: Please post any followups to this article. There's no point in keeping
this information a secret.