automatically (un)compress files with arbitrary suffix in emacs

Xournal, the note-taking app I’m using on my tablet, has the nice feature of gzipping its xml-format files. The following snippet in ~/.emacs will allow emacs to automatically compress/uncompress it during writing/reading.

(add-to-list 'jka-compr-compression-info-list 
  ["\\.xoj" 
   "compressing" "gzip" ("-c" "-q") 
   "uncompressing" "gzip" ("-c" "-q" "-d") 
   t nil 
   "\213"]
 )
(jka-compr-update)