DefaultModality
DefaultModality is a backwards compatible extension of the attendee id (UUID string) and session token schemas (base 64 string). It appends #
For example, attendeeId: "abcdefg" contentAttendeeId: "abcdefg#content" base(contentAttendeeId): "abcdefg" modality(contentAttendeeId): "content" hasModality(contentAttendeeId): true