Instead of e.g. http://lv2plug.in/ns/lv2core#ControlPort you can just write lv2:ControlPortThat I understand. But: 1. The logic that allows this is hard coded in the LV2 host, it is not the result of 'including' the @prefix. Checking that the @prefix is present does not mean that whatever is hard coded corresponds to what the @prefix is supposed to imply. This is what I mean when saying that all this just provides 'an illusion of conformity'.
@prefix is just turtle language. It's nearly the first you read about in the introduction for RDF 1.1 Turtle