New custom option for overriding mailcap choices

* lisp/net/mailcap.el (mailcap--get-user-mime-data): New function.
(mailcap--set-user-mime-data): New function.
(mailcap-user-mime-data): New customization option.
(mailcap-select-preferred-viewer): New function.
(mailcap-mime-info): Use it.

* doc/misc/emacs-mime.texi (mailcap): Document `mailcap-user-mime-data'.

1 files changed, 5 insertions, 0 deletions

diff --git a/doc/misc/emacs-mime.texi b/doc/misc/emacs-mime.texi
index c9c4b7c2a2f..2b3bba39ad9 100644
--- a/doc/misc/emacs-mime.texi
+++ b/doc/misc/emacs-mime.texi
@@ -1826,6 +1826,11 @@ matching types.
 @vindex mailcap-mime-data
 This variable is an alist of alists containing backup viewing rules.
 
+@item mailcap-user-mime-data
+@vindex mailcap-user-mime-data
+A customizable list of viewers that take preference over
+@code{mailcap-mime-data}.
+
 @end table
 
 Interface functions: