[squid-users] urlgroup usage weirdness

I just fail to understand how can I use the urlgroup's in squid. I
just wrote a url_rewrite program, which returns something like
'!porn!http://previous.url' on matched queries. I added this to squid
config:

acl porn urlgroup porn
acl classes src some.dotted.quad.and/mask

http_access deny porn
http_access allow classes

... and this seems not to work. If i strip out the second
'http_access' directive squid blocks access totally.

What have I done wrong? Is there some example on using urlgroup's?

Also, can I specify more that one urlgroup when returning result from
url_rewriter?

-- 
Sphinx of black quartz judge my vow!