[squid-users] Could you describe about "adaptation_service_set" statement a bit more.

[S.KOBAYASHI]

Hello developer,

I'm using a squid  3.HEAD-20080711 and using ICAP as well. 
Now I have a question. The sample mentioned as below.
adaptation_service_set svcBlocker urlFilterPrimary urlFilterBackup

When will be second icap service used instead of first one?

Thanks a lot,
SEIJI KOBAYASHI