I've been reading about Webhooks and I'm trying to determine if it's a specification vs a style/pattern.

By "specification" I mean that the implementation details, e.g. headers, payload and so on are well defined. By "style" or "pattern" I mean in the sense that REST is a style (as opposed to a spec) or a pattern which describes usage but doesn't define implementation details.

From what I see, Webhooks is a style/pattern. That the event(s) which triggers the http callbacks are generated however the developer wants, and that the http callbacks have no specific implementation requirements except to be an http post.

Is this correct?