$nick(#mIRC,0) according to the help file, returns the total number of nicknames on #mIRC
However I have found that in 6.17 and in 6.21 it actually returns the color code char (ctrl+K) before the number.
example:
There are 3 ops, 1 voiced and 3 regular users on #mIRC.
echo $nick(#mIRC,0,a,o) non ops present
will return
"
non ops present"
instead of
"4 non ops present"