zephyr-hook-list documentation

zephyr-hook-list's default value is
   '(zephyr-parse
     zephyr-dispatch
     zephyr-parse-fields
     zephyr-add-banner
     zephyr-insert) 

Documentation:
A list of functions to call to process an incoming message.  A lot
of customization can be done by changing this list.  For example, to
visibly timestamp messages, add the function zephyr-add-timestamp next
to zephyr-add-banner.  This list forms a pipeline; each function takes 
a message as its argument and returns a message as its result.  If a 
function returns nil, processing stops.

These functions are called once per message.  To run functions once 
for each buffer in which the message is inserted, see
zephyr-insert-hook-list.