Custom endpoints, process engine necessary? how to use path different than engine-rest?

I found out that for the process engine with path /engine-rest it us used jax-rs jersey. I was able to add some additional custom endpoints e.g. localhost:port/engine-rest/customendpoint

But I am wondering how can I do instead localhost:port/customendpoint?

Actually I dont know if I would need the process engine for my endpoints at all.

How does it technically work to have endpoints which are separate from process engine or from camunda web? At the moment I just did addAdditionalResources in an jerseyConfig class. That added my endpoint to the process engine.

How does the separation of camunda web and process engine work?

Are these kind of own applications with no intersection of url paths?