$nick($chan,0) or $nick($chan,0,a) for the total number of nicks in $chan
$nick($chan,0,r) for the number of regular (non-opped/voiced/half-opped) users
$nick($chan,0,o) for the number of ops
$nick($chan,0,v) for the number of voiced users
$nick($chan,0,ov) for the number of ops + voiced users
$nick($chan,0,h) for the number of halfops
$nick($chan,0,hv) for the number of halfops + voiced users
$nick($chan,0,ohv) or $nick($chan,0,a,r) for all non-regular users