How do you use mailcap-mime-data?

How do you use mailcap-mime-data?

[Eric Abrahamsen]

I've been trying for a while to get Emacs to use xdg-open when opening
any/all files in an external program: I don't want to have to maintain
duplicate file/program associations both inside Emacs and on my system.
(I'm on arch linux, no DE.)

That includes attachments in Gnus. I have this in my setup:

(setq mailcap-mime-data
      '(("application" (".*" (viewer . "xdg-open %s")))))

Which presumably the internet told me at some point was the right thing
to do.

This causes some failures, however, because there's no `type' key in the
assoc list. The `mailcap-mime-types' function expects all entries to
have a `type' key with a string value, and blows up otherwise.

The docstring of `mailcap-mime-data' doesn't mention a `type' key,
though the default values all have it.

My question(s) is/are:

1. Should I be doing this some other way?
2. Should the `mailcap-mime-data' docstring mention the `type' key?
3. Should `mailcap-mime-types' check for a nil `type' key and not barf?
4. Why, after manually setting `mailcap-mime-data', does it now have the
   below value?

Help with any/all of these questions much appreciated!

(("audio"
  (".*"
   (viewer . "/usr/bin/xdg-open %s")
   (type . "audio/*")))
 ("image"
  (".*"
   (viewer . "/usr/bin/xdg-open %s")
   (type . "image/*")))
 ("text"
  ("html"
   (viewer . "/usr/bin/xdg-open %s ")
   (type . "text/html")
   ("copiousoutput" . t)))
 ("application"
  ("msword"
   (viewer . "/usr/bin/xdg-open %s")
   (type . "application/msword"))
  ("pdf"
   (viewer . "/usr/bin/xdg-open %s")
   (type . "application/pdf"))
  ("postscript"
   (viewer . "/usr/bin/xdg-open %s")
   (type . "application/postscript"))
  (".*" (viewer . "xdg-open %s"))))