I would think that a carrier between any citypair would mean 'travel must be via' this carrier only (marketing flt no - no operating carrier).
For example, the first one:
BKK(UL)HKG-SEL-LAX(UA)SFO
Means routing is valid if UL is used between BKK-HKG, any carrier between SEL-LAX, and only UA LAX-SFO. Same thing goes if more than one carrier specified.
Ok, thanks.
But, here's a question... what if you go BKK-SEL-SFO and skip HKG and LAX... what are the restrictions on BKK-SEL? UL only, or OZ (the fare airline)? Same question for SEL-SFO. Thanks.