Endpoints use the exchange of Setup messages to negotiate MOQT extensions. Extensions can define new Message types, new Parameters, or new framing for Data Streams and Datagrams.
The client and server MUST include all Setup Options Section 9.4.1 required for the negotiated MOQT version in SETUP.
Each endpoint declares the extensions it supports and provides any initial values required by those extensions as Setup Options in SETUP. Once an endpoint has both sent and received SETUP messages, it determines the set of negotiated extensions.
New versions of MOQT MUST specify which existing extensions can be used with that version. New extensions MUST specify the existing versions with which they can be used.