bug#23184: 25.0.92; User-friendly way to override doc-view-mode as MIME viewer

[Eli Zaretskii <eliz@gnu.org>]

> From: Teemu Likonen <tlikonen@iki.fi>
> Date: Sat, 09 Apr 2016 12:27:38 +0300
> Cc: 23184@debbugs.gnu.org
> 
> > (2) Or maybe we could add a customizable list `mailcap-user-mime-data'
> >     (better name welcome) which would override `mailcap-mime-data',
> >     i.e., if a viewer is specified there, then `mailcap-mime-data' with
> >     the heuristics around it won't even be consulted.
> 
> > Any better suggestions?  If not, I can do that.  (In case I'd implement
> > that, should that go only into master or emacs-25?)
> 
> I don't oppose mailcap-user-mime-data but I think user shouldn't be
> forced to duplicate his mailcap configuration inside Emacs.

Does that suggestion really require duplication, or does it require to
have only those (hopefully few) entries that override the default?

> User already has his system's mailcap settings and many programs
> respect that. Why doesn't Emacs? (Ok, it does but with its own
> preferences of doc-view-mode etc.)

Because doc-view-mode is specific to Emacs?

> How about a variable like mailcap-prefer-system-mailcap with a non-nil
> value would put the priority of doc-view-mode (and every viewer Emacs
> offers) below system's mailcap configuration?

That'd still require a separate customization in Emacs, so I wonder
how it is better than what Tassilo proposed.