Additional information about which detailed type of SSM this is.
Legal values
NEW Inserts new flight (leg) information.
CNL Deletes all flight (leg) information in the given period matching the given ScheduleFlightDays / ScheduleFlightWeeks) (Nothing in the future will depend on the cancelled/deleted data.)
SKD Deletes all flight (leg) information in the given period. The end data is not mandatory. (Nothing in the future will depend on the cancelled/deleted data.)
The description of the values above is standard IATA. Systems can implement different rules, for instance handling NEW as an update if the flight leg exist, or handling RPL and RRT the same.
