From Valve Developer Community
- Player entered/exited the vehicle. (activator is the player)
- Player pressed the +attack/+attack2 key
- State of attack/attack2 button. Also called when the player exits the vehicle.
- These Outputs each fire in response to the firing of the like-numbered
FireUser4Input; see User Inputs and Outputs.
OnKilled(Only in the Left 4 Dead series)
- This Output fires when the entity is killed and removed from the game.