Never had carry on bags weighed or sized on international or domestic. However, on occasions, only when in Y, I have been asked to show/hold up my carry on to the check in agent, presumably to visually assess if it meets requirements. They also seem to go through periods of trying to make people attach hand baggage tags to luggage; no idea why. I have never been checked at the boarding gates for carry on, even when blatantly breaking the limits for size/weight and number of bags.