List of vectors that describe available compression techniques.
Each element, which describes a compression technique, is a vector of
the form [REGEXP COMPRESS-MSG COMPRESS-PROGRAM COMPRESS-ARGS
UNCOMPRESS-MSG UNCOMPRESS-PROGRAM UNCOMPRESS-ARGS
APPEND-FLAG STRIP-EXTENSION-FLAG FILE-MAGIC-CHARS], where:
regexp is a regexp that matches filenames that are
compressed with this format
compress-msg is the message to issue to the user when doing this
type of compression (nil means no message)
compress-program is a program that performs this compression
(nil means visit file in read-only mode)
compress-args is a list of args to pass to the compress program
uncompress-msg is the message to issue to the user when doing this
type of uncompression (nil means no message)
uncompress-program is a program that performs this compression
uncompress-args is a list of args to pass to the uncompress program
append-flag is non-nil if this compression technique can be
strip-extension-flag non-nil means strip the regexp from file names
before attempting to set the mode.
file-magic-chars is a string of characters that you would find
at the beginning of a file compressed in this way.
If you set this outside Custom while Auto Compression mode is
already enabled (as it is by default), you have to call `jka-compr-update' after setting it to properly update other variables. Setting this through Custom does that automatically.