Seen that, done that. I'm still waiting some clues - or some docs.......
( I am using l7filter on at least one linux machine, and it works just fine, actually on Coyote and Brazil FW.)
It is not very hard:
define layer7 protocol, for example:
/ip firewall layer7-protocol
add comment="" name="ftp" regexp="^220[\\x09-\\x0d -~]*ftp"
after that you can create firewall rule with your newly defined layer7 protocol.
Well, easier said than done. Did you tried it ? Cause I first tried and only after I asked. I does not appear as I can use it anywhere in the filter. Autocompletion in CLI or winbox interface does not show any of the defined protocols/classifiers. If you have 1 (one at least)
working example, show it here. If it's hidden..... my mistake. And give another name please to the protocol..... let's say for yahoo messenger. Or else.