From XEP-45 7.2.3
As shown in the last stanza, the "self-presence" sent by the room to the new user MUST include a status code of 110 so that the user knows this presence refers to itself as an occupant. This self-presence MUST NOT be sent to the new occupant until the room has sent the presence of all other occupants to the new occupant; this enables the new occupant to know when it has finished receiving the room roster.
The service MAY rewrite the new occupant's roomnick (e.g., if roomnicks are locked down or based on some other policy).
If the user has connected using a MUC client (as indicated on joining the room by inclusino of the MUC extension), then the service MUST allow the client to enter the room, modify the nick in accordance with the lockdown policy, and include a status code of "210" in the presence broadcast that it sends to the new occupant.