set banner_expand [on|off|toggle]
If ON: The value of set banner is run through expando-substution every
time it is used.
If OFF: The value of set banner is taken as a literal string.
This is useful if you like to display the current time ($Z) in your banner.
/set banner_expand ON
/set banner $Z ***
9:00PM *** CTCP PING from MrFoo detected