Originally Posted by br2k

As far as I can tell, only passengers with priority boarding can bring larger bags on board.

It is enforced - in a sense that passengers with larger bags are not allowed to go through during priority boarding, and passengers that enter after priority boarding has ended must have yellow tags attached to their bags. Those tags signify that the bag needs to be placed in the cart.

I did not see anyone try to bring a bag with that tag on board. Every flight had flight manager standing by the door checking things, so I am guessing tagged bags would not be allowed on board.

I suppose one could try to rip the tag off between getting on and off the bus, but the tag is not easily removed so it'd be pretty obvious, and they do check boarding passes at boarding time as well (and priority boarding is clearly marked on BP).