I see in the fare rules of many HKG-EWR/JFK tickets that allow one stopover in ORD. However, when I tried booking such a flight (e.g. HKD-EWR-ORD-HKG), it doesn't allow me to do so. Is there any trick? I know that the flight between EWR and ORD should be operated by AA. Can the flight be booked as a codeshared flight in this case?