All clients see the same message order from the server. All messages are sent to all users. Aside from the presence messages sent by the server, messages are sent by users.
All messages in a room have a unique sequence number (0, 1, ...). Sequence numbers are implicit, as We assume that the server may not be aware is unaware of them sequence numbers (e.g. XMPP MUC); clients must allocate them implicitly when receiving messages. This version of the spec does ''not'' support servers that give explicit sequence numbers to messages; this would force us to handle the case where messages are received with explicitly out-of-order sequence numbers. For now, we rely on transcript consistency to detect out-of-order messages for the ''implicit'' sequence number case.
A new user synchronizes his view of sequence numbers via the QUERY / MEMBER_LIST messages (see below).