The unrealircd.org/userip message tag communicates the original user@ip
to IRC Operators so they can see the IP address of users even if cloaking is
active. Normal users will not see this tag, only IRCOps.

Syntax of the tag:
unrealircd.org/userip=<user>@<ip>

Example line:
@unrealircd.org/userip=~user@127.0.0.1 :nick!~user@Mask-ABCDEF PRIVMSG #test :hi

See also other IRCOp-only "informative" message tags:
* unrealircd.org/userip
* unrealircd.org/geoip