The user has been banned from the room, and is no longer allowed to join it until they are un-banned from the room (by having their membership state set to a value other than ban).
The user has been invited to join a room, but has not yet joined it. They may not participate in the room until they join.
The user has joined the room (possibly after accepting an invite), and may participate in it.
The user has knocked on the room, requesting permission to participate. They may not participate in the room until they join.
The user was once joined to the room, but has since left (possibly by choice, or possibly by being kicked).
Well-known values (from the spec or MSCs) that are allowed in the Membership type.