To use, for instance, `untar' to unpack tar files and `zip -x' to
unpack zip files, say the following:
(setq gnus-uu-user-archive-rules
- '((\"\\\\.tar$\" \"untar\")
+ \\='((\"\\\\.tar$\" \"untar\")
(\"\\\\.zip$\" \"zip -x\")))"
:group 'gnus-extract-archive
:type '(repeat (group regexp (string :tag "Command"))))