When the mechanism defined by this specification has been negotiated,
sending a RTP packet that has any CSRCs or contains any {[RFC8285](https://datatracker.ietf.org/doc/rfc8285/)}}
header extensions follows the steps below. This mechanism MUST NOT
be used with header extensions other than the [[RFC8285](https://datatracker.ietf.org/doc/rfc8285/)] variety.
Likely Markdown nit: {RFC8285}}