Spell/Ability in event handler

[Oni]

Is it possible to cast a spell or ability in an event handler?

If I am registered to say listen to the messages that are coming out on a party channel could I then immediatley Assist if a "help me I'm about to die" message goes out?

[Gello]

Assist you can do in response to an event. Targeting is also fine.

Using a spell or ability in general you can't. You can't for instance react to UNIT_HEALTH and automatically cast heals.