Config question

This is the sample config and comments on my system. What exactly does the {::1}
mean?

Is this some sort of LISP or M4 syntax? Sorry, I am not too familiar
with LISP yet.

Thanks,

brian

# Exim configuration string to run before running SA against the message
# This decides whether SA gets run against the message or not.  This
# default will not reject messages if the message had SA headers but
# they weren't added by us.

SAEximRunCond: ${if and {{def:sender_host_address} {!eq {$sender_host_address}{127.0.0.1}} {!eq {$sender_host_address}{::1}}}}
-- 
Brian Lavender
http://www.brie.com/brian/