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What exactly do they mean? I'm trying to code the Seagallop Ferries into my hack, and I'm not entirely sure if I need to alter or remove any instances thereof as I add Seagallop-related events and such.
They are macros defined in macros/event_macros.asm to deal with event flags. They are meant to be used when the flag address has been already loaded to check a previous flag, so you can skip the ld hl instruction. If they look confusing to you, they are in practice the same as CheckEvent and SetEvent, so you can just use those.