Is it/will it be possible for a single interaction to have multiple targets/means of selecting targets? For example, could I mod in an interaction that paralyzes a target on line-of-sight, but makes the caster dizzy/drowsy as a sort of backlash?
It looks like interactions are set up to allow multiple targets with different effects for each. However, I'm not sure how an interaction would be made self-targeting. Shot in the dark, but maybe SELF instead of LINE_OF_SIGHT in the CDI:TARGET tag?
It's sort of weird how the interaction def is split between the INTERACTION block and the CE_CAN_DO_INTERACTION. I guess the idea is that certain interaction attributes only make sense when the interaction is being performed by a creature.
I also can't tell from those raws how "native" interactions are handled, i.e. a native ability to perform an interaction without getting the ability from a syndrome. Maybe creature effect (CE) stuff can just be included in a creature def as well as a syndrome def?
From the look of the werebeast, the werebeast's bite attack (in the creature def) needs a line telling it to use an interaction. "Native" interactions are probably handled similarly (technically in the werebeast's case the bite is a "native" interaction because it isn't caused by the syndrome, but instead a part of creature def).
As for the CE_CAN_DO_INTERACTION, it seems to add the interaction to the creature similar to how adding SPECIALATTACK_INTERACTION:WEREBEAST_BITE to the creature's bite attack gives the bite attack an associated interaction. As a result it needs to define more specifically how the interaction is done.
As for why part of the interaction is in the interaction definition and the other half is under the CE_CAN_DO_INTERACTION tag is sort of clever.
I would assume this is because the interaction can be used in more that one way. For example, say there is a creature that can raise zombies like a necromancer, but instead of line of sight it is an area effect. Instead of rewriting the interaction a second time you just link CE_CAN_DO to the same interaction, but define the attack differently. This way the interaction is more user friendly to other creatures and modders. IIRC this is called the Adapter Pattern. HUZZAH FOR DESIGN PATTERNS!