ReadonlycontentReadonlyeventReadonlymediaReadonlymimeReadonlysessionReadonlytrackThe track that initiated this session, captured when the session was created. Carried on the props (not read from controller state at message time) so concurrent license exchanges for different tracks each attribute to their own track.
The MIME and content type of the session's content, captured at creation so the license span can distinguish the certificate exchange from the per-content-type license exchanges.