though this discuss is a year old, it's amazingly useful to me at this time in 2012. And I can only say 'THANK YOU and GOD BLESS'
@lossendae and togi_one: the solution only works where there is some entry but a wrong type. Say, text where you should have numbers. I would like to have a situation where the red borderline is enabled when there is an error in that field, whether empty or taking a wrong value.
I tried [[+fi.error.first_name:then=` warning`]], that didn't help