Rules versus preferences
The never-pair list is a hard rule: the engine is not allowed to produce a schedule that pairs a listed combination together, full stop. Must-pair and crew preference are the opposite, they're accommodated when the puzzle allows it, but they can lose to a stronger rule or to seniority. Domestic-only sits with the rules: it's a hard restriction on which lines a pilot can be assigned to, not a preference.
Never-pair list Hard rule
Must-pair list Accommodated, not guaranteed by this filter
Domestic-only Hard rule
Pilot
Domestic only
SOE: supervised operating experience Hard rule
New and newly upgraded pilots must be paired with a training captain until their SOE is signed off. Training captains are designated on the Seniority Lists page; the designation applies regardless of aircraft type. List anyone currently under SOE here and the engine will only pair them with a training captain.