This event is fired immediately whenever you cast a spell, as well as every second while you channel spells.
- The spell you cast doesn't need to have any explicit "cooldown" of its own, since this event also triggers off of anything that incurs a GCD (global cooldown). In other words, it basically fires whenever you cast any spell or channel any spell.
- (It may possibly even trigger from spells that are "off the GCD" and which don't have any cooldown of their own; but there's no way to verify that, since all spells in game that are "off the GCD" are special class "burst" abilities with long cooldowns.)
- It's worth noting that this event does NOT fire when spells finish their cooldown!
- Whenever you cast a spell, this event triggers twice in a row. Most likely to signal that a spell cast has begun, and then to signal that the GCD has been triggered.
- When a hunter auto-shoots, they're actually casting the "Auto Shot" spell (which repeatedly auto-casts itself until cancelled, and has a cooldown of its own, but is otherwise completely "off the GCD" and doesn't trigger the GCD at all when it's cast/shooting/aborted). So every time the hunter shoots a projectile, this event will fire to signal that the "Auto Shot" spell has begun its internal cooldown. Note that this behavior is unique to "Auto Shot"; and that the regular melee spell "Attack" (or melee swings) do NOT trigger this event.
- Furthermore, any channeled spells will fire this event once per second while the channeling is ongoing. As an example, if you cast Volley, this event first fires once to signal that a spell with a cooldown (Volley) has been cast. Then it immediately fires again to signal that channeling of Volley has begun. And after that, it fires every second while the channeling is ongoing.