(usr-tc) "_"command

Does anyone have a list of command which begin with "_", the only one I know is "_authentication". I think all these command should be very helpful for troubleshooting. Any idea is appreciated. - To unsubscribe to usr-tc, send an email to "majordomo@xmission.com" with "unsubscribe usr-tc" in the body of the message. For information on digests or retrieving files and old messages send "help" to the same address. Do not use quotes in your message.