Below are some examples.
Don't have mIRC right here now, but I think this should be correct.
From Help:
$istok(text,token,C)
False:
var %line = some/text/with/many/in/it
echo -a $istok(%line,$chr(47),32)
True:
var %line = some / text / with / many / in / it
echo -a $istok(%line,$chr(47),32)
True:
var %line = some/text/with/many/in/it
echo -a $iif(($chr(47) isin %line),True,False)