In Fielding’s REST, the exchange is defined in terms of the document contents (the content types). These are what define the interaction both ways, both in terms of data and in terms of navigating the set and interacting with it (think links and forms).

The client necessarily has to know about that. That’s where the coupling happens. Where the coupling doesn’t happen is in things like resource names and locations, as far as Fielding’s thesis was concerned there’s only one location the client needs to know and it’s the root location, everything else can be obtained by navigating the service.