I can confirm that persistent area damage.does behave like
However, while discussing this with Frank (our resident game-file diver), it became apparent that we're still not accurately documenting damagetypes.
There's the original engine-level damage type system and a relatively new script-level damage type system. Crowstorm deals spellaoe on an engine-level. Spellvamp, Gunblade, etc, interacts with engine-level damage types, which is why Crowstorm heals for one-third effectiveness.
However, Riot added a script-level system that interacts with runes and other more modern effects. Possible tags include: aoe, periodic, indirect, basicattack, activepsell, proc, pet and nonredirectable. Crowstorm has at least aoe and period (didn't ask for the full list). An effect like Arcane Comet just has a priority system - so abilities with both aoe and periodic will prioritize the periodic behavior.
Both the engine-level and script-tags are to be assigned arbitrarily by a Riot engineer and there's no guarantee they will match. There could be a engine-level single target ability with the aoe script-tag. We can hope that our current spelleffects options cover all possible outcomes - but in the future it might ultimately be necessary to have separate
|scripttags= in the future.
However, this shouldn't affect the current project. Currently, 'aoedot' is the only non-engine type supported by "spelleffects". So if we do need to update it in the future, spelleffects is already the same as enginedamage except for abilities with the aoedot type - so updating that short list shouldn't be too hard.