Several people have suggested (Xidorn, Roland) that there should be a value (possibly called auto, or alternate),
that alternates between 'over' and 'under' when the ruby has multiple levels of interlinear annotation.

My [Xidorn’s] proposal is: This value is not computed to anything else. And during the
positioning, this value is equal to "over" for rtc in odd indexes, and "under" for rtc in even indexes.

Overall, it sounds reasonable to [fantasai], but I think we should have a way to specify the first level, rather than always being over. Maybe [ over | under ] || alternate instead? Or something else?

This value should probably be the initial value.