Quake III Networking Model Question

I am studying the Quake III and Source Engine networking model, and one of the things I am not understanding is how to send events, such as throwing or throwing a grenade?

Knowing that, for example, Counter Strike has a fixes send rate from the server to the client, how the events are packed inside snapshots before being sent?

Since the events, different from properties such as life, that exist throughout the execution of the game.

Is there any documentation or source code that demonstrates how this is done?