Affiliation -- a long-lived association or connection with a room; the possible affiliations are "owner", "admin", "member", and "outcast" (naturally it is also possible to have no affiliation); affiliation is distinct from role. An affiliation lasts across a user's visits to a room.

Ban -- to remove a user from a room such that the user is not allowed to re-enter the room (until and unless the ban has been removed). A banned user has an affiliation of "outcast".

Bare JID -- the <user@host> by which a user is identified outside the context of any existing session or resource; contrast with Full JID and Room JID.

Full JID -- the <user@host/resource> by which an online user is identified outside the context of a room; contrast with Bare JID and Room JID.

GC -- the minimal "groupchat 1.0" protocol http://www.jabber.org/protocol/groupchat.html developed within the Jabber community in 1999; MUC is backwards-compatible with GC.

History -- a limited number of message stanzas sent to a new occupant to provide the context of current discussion.

Invitation -- a special message sent from one user to another asking the recipient to join a room.

IRC -- Internet Relay Chat.

Kick -- to temporarily remove a participant or visitor from a room; the user is allowed to re-enter the room at any time. A kicked user has a role of "none".

Logging -- storage of discussions that occur within a room for public retrieval outside the context of the room.

Member -- a user who is on the "whitelist" for a members-only room or who is registered with an open room. A member has an affiliation of "member".

Moderator -- a room role that is usually associated with room admins but that may be granted to non-admins; is allowed to kick users, grant and revoke voice, etc. A moderator has an role of "moderator".

MUC -- the multi-user chat protocol for text-based conferencing specified in this document.

Occupant -- any Jabber user who is in a room (this is an "abstract class" and does not correspond to any specific role).

Outcast -- a user who has been banned from a room. An outcast has an affiliation of "outcast".

Participant -- an occupant who does not have administrative privileges; in a moderated room, a participant is further defined as having voice (in contrast to a visitor). A participant has a role of "participant".

Private Message -- a message sent from one occupant directly to another's room JID (not to the room itself for broadcasting to all occupants).

Role -- a temporary position or privilege level within a room, distinct from a user's long-lived affiliation with the room; the possible roles are "moderator", "participant", and "visitor" (it is also possible to have no defined role). A role lasts only for the duration of an occupant's visit to a room.

Room -- a virtual space that Jabber users figuratively enter in order to participate in real-time, text-based conferencing with other users.

Room Administrator -- a user empowered by the room owner to perform administrative functions such as banning users; however, is not allowed to change defining room features. An admin has an affiliation of "admin".

Room ID -- the node identifier portion of a Room JID, which may be opaque and thus lack meaning for human users (see Business Rules for syntax); contrast with Room Name.

Room JID -- the &ROOMJID; by which an occupant is identified within the context of a room; contrast with Bare JID and Full JID.

Room Name -- a user-friendly, natural-language name for a room, configured by the room owner and presented in Service Discovery queries; contrast with Room ID.

Room Nickname -- the resource identifier portion of a Room JID (see Business Rules for syntax); this is the "friendly name" by which an occupant is known in the room.

Room Owner -- the Jabber user who created the room or a Jabber user who has been designated by the room creator or owner as someone with owner privileges (if allowed); is allowed to change defining room features as well as perform all administrative functions. An owner has an affiliation of "owner".

Room Roster -- a Jabber client's representation of the occupants in a room.

Server -- a Jabber server that may or may not have associated with it a text-based conferencing service.

Service -- a host that offers text-based conferencing capabilities; often but not necessarily a sub-domain of a Jabber server (e.g., conference.jabber.org).

Subject -- a temporary discussion topic within a room.

Visit -- a user's "session" in a room, beginning when the user enters the room (i.e., becomes an occupant) and ending when the user exits the room.

Visitor -- in a moderated room, an occupant who does not have voice (in contrast to a participant). A visitor has a role of "visitor".

Voice -- in a moderated room, the privilege to send messages to all occupants.

Fully-Anonymous Room -- a room in which the full JIDs or bare JIDs of occupants cannot be discovered by anyone, including room admins and room owners; such rooms are NOT RECOMMENDED or explicitly supported by MUC, but are possible using this protocol if a service implementation offers the appropriate configuration options; contrast with Non-Anonymous Room and Semi-Anonymous Room.

Hidden Room -- a room that cannot be found by any user through normal means such as searching and service discovery; antonym: Public Room.

Members-Only Room -- a room that a user cannot enter without being on the member list; antonym: Open Room.

Moderated Room -- a room in which only those with "voice" may send messages to all occupants; antonym: Unmoderated Room.

Non-Anonymous Room -- a room in which an occupant's full JID is exposed to all other occupants, although the occupant may choose any desired room nickname; contrast with Semi-Anonymous Room and Fully-Anonymous Room.

Open Room -- a room that anyone may enter without being on the member list; antonym: Members-Only Room.

Password-Protected Room -- a room that a user cannot enter without first providing the correct password; antonym: Unsecured Room.

Persistent Room -- a room that is not destroyed if the last occupant exits; antonym: Temporary Room.

Public Room -- a room that can be found by any user through normal means such as searching and service discovery; antonym: Hidden Room.

Semi-Anonymous Room -- a room in which an occupant's full JID can be discovered by room admins only; contrast with Fully-Anonymous Room and Non-Anonymous Room.

Temporary Room -- a room that is destroyed if the last occupant exits; antonym: Persistent Room.

Unmoderated Room -- a room in which any occupant is allowed to send messages to all occupants; antonym: Moderated Room.

Unsecured Room -- a room that anyone is allowed to enter without first providing the correct password; antonym: Password-Protected Room.

Most of the examples in this document use the scenario of the witches' meeting held in a dark cave at the beginning of Act IV, Scene I of Shakespeare's Macbeth, represented here as the "darkcave@macbeth.shakespeare.lit" chatroom. The characters are as follows:

There are four defined roles that an occupant may have:

1. Moderator
2. Participant
3. Visitor
4. None (the absence of a role)

Roles are temporary in that they do not necessarily persist across a user's visits to the room and MAY change during the course of an occupant's visit to the room. An implementation MAY persist roles across visits and SHOULD do so for moderated rooms (since the distinction between visitor and participant is critical to the functioning of a moderated room).

There is no one-to-one mapping between roles and affiliations (e.g., a member could be a participant or a visitor).

A moderator is the most powerful occupant within the context of the room, and can to some extent manage other occupants' roles in the room. A participant has fewer privileges than a moderator, although he or she always has the right to speak. A visitor is a more restricted role within the context of a moderated room, since visitors are not allowed to send messages to all occupants.

Roles are granted, revoked, and maintained based on the occupant's room nickname or full JID rather than bare JID. The privileges associated with these roles, as well as the actions that trigger changes in roles, are defined below.

Information about roles MUST be sent in all presence stanzas generated or reflected by the room and thus sent to occupants.

There are five defined affiliations that a user may have in relation to a room:

1. Owner
2. Admin
3. Member
4. Outcast
5. None (the absence of an affiliation)

These affiliations are long-lived in that they persist across a user's visits to the room and are not affected by happenings in the room. In addition, there is no one-to-one mapping between these affiliations and an occupant's role within the room. Affiliations are granted, revoked, and maintained based on the user's bare JID.

If a user without a defined affiliation enters a room, the user's affiliation is defined as "none"; however, this affiliation does not persist across visits (i.e., a service does not maintain a "none list" across visits).

The member affiliation provides a way for a room owner or admin to specify a "whitelist" of users who are allowed to enter a members-only room. When a member enters a members-only room, his or her affiliation does not change, no matter what his or her role is. The member affiliation also provides a way for users to effectively register with an open room and thus be lastingly associated with that room in some way (one result may be that the user's nickname is reserved in the room).

An outcast is a user who has been banned from a room and who is not allowed to enter the room.

Information about affiliations MUST be sent in all presence stanzas generated or reflected by the room and sent to occupants.

A Jabber entity may wish to discover if a service implements the Multi-User Chat protocol; in order to do so, it sends a service discovery information ("disco#info") query to the component's JID:

The service MUST return its identity and the features it supports:

Note: Because MUC is a superset of the old "groupchat 1.0" protocol, a MUC service SHOULD NOT return a <feature var='gc-1.0'/> entry in a disco#info result.

The service discovery items ("disco#items") protocol enables a user to query a service for a list of associated items, which in the case of a chat service would consist of the specific chat rooms hosted by the service.

The service SHOULD return a full list of the rooms it hosts.

If the full list of rooms is large (see XEP-0030 for details), the service MAY return only a partial list of rooms.

Using the disco#info protocol, a user may also query a specific chat room for more detailed information about the room. A user SHOULD do so before entering a room in order to determine the privacy and security profile of the room configuration (see the Security Considerations for details).

The room MUST return its identity and SHOULD return the features it supports:

Note: Because MUC is a superset of the old "groupchat 1.0" protocol, a MUC room SHOULD NOT return a <feature var='gc-1.0'/> entry in a disco#info result. The room SHOULD return the materially-relevant features it supports, such as password protection and room moderation (these are listed fully in the feature registry maintained by the XMPP Registrar; see also the XMPP Registrar section of this document).

A chatroom MAY return more detailed information in its disco#info response using &xep0128;, identified by inclusion of a hidden FORM_TYPE field whose value is "http://jabber.org/protocol/muc#roominfo". Such information might include a more verbose description of the room, the current room subject, and the current number of occupants in the room:

Some extended room information may be dynamically generated (e.g., the URL for discussion logs, which may be based on service-wide configuration) whereas other information may be based on the room configuration.

Note: The foregoing extended service discovery fields for the 'http://jabber.org/protocol/muc#roominfo' FORM_TYPE may be supplemented in the future via the mechanisms described in the Field Standardization section of this document.

A user MAY also query a specific chat room for its associated items:

An implementation MAY return a list of existing occupants if that information is publicly available, or return no list at all if this information is kept private.

Note: These <item/> elements are qualified by the disco#items namespace, not the muc namespace; this means that they cannot possess 'affiliation' or 'role' attributes, for example.

If a non-occupant attempts to send a disco request to an address of the form &ROOMJID;, a MUC service SHOULD return the request to the entity and specify a &badrequest; error condition. If an occupant sends such a request, the service MAY pass it through the intended recipient; see the Implementation Guidelines section of this document for details.

A Jabber user may want to discover if one of the user's contacts supports the Multi-User Chat protocol. This is done using Service Discovery.

The client SHOULD return its identity and the features it supports:

A user may also query a contact regarding which rooms the contact is in. This is done by querying the contact's full JID (<user@host/resource>) while specifying the well-known Service Discovery node 'http://jabber.org/protocol/muc#rooms':

Optionally, the contact MAY include its roomnick as the value of the 'name' attribute:

In order to exit a multi-user chat room, an occupant sends a presence stanza of type "unavailable" to the &ROOMJID; it is currently using in the room.

The service MUST then send presence stanzas of type "unavailable" from the departing occupant's room JID to the full JIDs of the departing occupant and of the remaining occupants:

Presence stanzas of type "unavailable" reflected by the room MUST contain extended presence information about roles and affiliations, and MAY also contain normal <status/> information (which enables occupants to provide custom exit messages if desired).

Normal presence stanza generation rules apply as defined in &xmppim;, so that if the user sends a general unavailable presence stanza, the user's server will broadcast that stanza to the &ROOMJID; to which the user's client has sent directed presence.

It is possible that a user may not be able to gracefully exit the room by sending unavailable presence directly to the room. If the user goes offline without sending unavailable presence, the user's server is responsible for sending unavailable presence on behalf of the user (in accordance with RFC 3921). If the user's server goes offline or connectivity is lost between the user's server and the MUC service to which the user is connected (e.g., in federated communications), the MUC service is responsible for monitoring error stanzas it receives in order to determine if the user has gone offline. If the MUC service determines that the user has gone offline, it must treat the user as if the user had itself sent unavailable presence.

Note: If the room is not persistent and this occupant is the last to exit, the service is responsible for destroying the room.

A common feature of multi-user chat rooms is the ability for an occupant to change his or her nickname within the room. In MUC this is done by sending updated presence information to the room, specifically by sending presence to a new room JID in the same room (changing only the resource identifier in the room JID).

The service then sends two presence stanzas to the full JID of each occupant (including the occupant who is changing his or her room nickname), one of type "unavailable" for the old nickname and one indicating availability for the new nickname.

The unavailable presence MUST contain the following as extended presence information in an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace:

• The new nickname (in this case, nick='oldhag')
• A status code of 303

This enables the recipients to correlate the old roomnick with the new roomnick.

If the user attempts to change his or her room nickname to a room nickname that is already in use by another user (or that is reserved by another user affiliated with the room, e.g., a member or owner), the service MUST deny the nickname change request and inform the user of the conflict; this is done by returning a presence stanza of type "error" specifying a &conflict; error condition:

However, if the bare JID (&BAREJID;) of the present occupant matches the bare JID of the user seeking to change his or her nickname, then the service MAY allow the nickname change. See the Nickname Conflict section of this document for details.

If the user attempts to change his or her room nickname but room nicknames are "locked down", the service MUST deny the nickname change request and return a presence stanza of type "error" specifying a ¬acceptable; error condition:

The user SHOULD then discover its reserved nickname as specified in the Discovering Reserved Room Nickname section of this document.

In multi-user chat systems such as IRC, one common use for changing one's room nickname is to indicate a change in one's availability (e.g., changing one's room nickname to "thirdwitch|away"). In Jabber, availability is of course noted by a change in presence (specifically the <show/> and <status/> elements), which can provide important context within a chatroom. An occupant changes availability status within the room by sending the updated presence to its &ROOMJID;.

The service then sends a presence stanza from the occupant changing his or her presence to the full JID of each occupant, including extended presence information about the occupant's role and full JID to those with privileges to view such information:

It can be useful to invite another user to a room in which one is an occupant. To do this, a MUC client MUST send XML of the following form to the &ROOM; itself (the reason is OPTIONAL and the message MUST NOT possess a 'type' attribute; the service MAY ignore or reject invites that possess a 'type' attribute):

The &ROOM; itself MUST then add a 'from' address to the <invite/> element whose value is the bare JID (or, optionally, the room JID) of the invitor and send the invitation to the invitee captured in the 'to' address (the service SHOULD include a message body explaining the invitation or containing the reason, for the sake of older clients; in addition, the room SHOULD add the password if the room is password-protected):

If the room is members-only, the service MAY also add the invitee to the member list. (Note: Invitation privileges in members-only rooms SHOULD be restricted to room admins; if a member without privileges to edit the member list attempts to invite another user, the service SHOULD return a &forbidden; error to the occupant; for details, see the Modifying the Member List section of this document.)

If the invitor supplies a non-existent JID, the room SHOULD return an ¬found; error to the invitor.

The invitee MAY choose to formally decline (as opposed to ignore) the invitation; and this is something that the sender may want to be informed about. In order to decline the invitation, the invitee MUST send a message of the following form to the &ROOM; itself:

It may be wondered why the invitee does not send the decline message directly to the invitor. The main reason is that certain implementations MAY choose to base invitations on room JIDs rather than bare JIDs (so that, for example, an occupant could invite someone from one room to another without knowing that person's bare JID). Thus the service MUST handle both the invites and declines.

Sometimes it is desirable to convert a one-to-one chat into a multi-user conference. The process flow is shown in the following examples.

First, two users begin a one-to-one chat.

Now the first person decides to include a third person in the discussion, so she (or, more precisely, her client) does the following:

1. Creates a new room
2. Optionally sends history of the one-to-one chat to the room
3. Sends an invitation to the second person and the third person, including a <continue/> flag.

Note: The new room SHOULD be non-anonymous, MAY be an instant room as specified in the Creating an Instant Room section of this document, and MAY have a unique room name received from the service as specified in the Requesting a Unique Room Name section of this document.

Note: Use of the Delayed Delivery protocol enables the room creator to specify the datetime of each message from the one-to-one chat history (via the 'stamp' attribute), as well as the JID of the original sender of each message (via the 'from' attribute). The room creator SHOULD send the complete one-to-one chat history before inviting additional users to the room, and SHOULD also send as history any messages appearing in the one-to-one chat interface after joining the room and before the second person joins the room; if the one-to-one history is especially large, the sending client may want to send the history over a few seconds rather than all at once (to avoid triggering rate limits). The service SHOULD NOT add its own delay elements (as described in the Discussion History section of this document) to prior chat history messages received from the room owner.

Note: Since the invitor's client knows the full JID of the person with whom the invitor was having a one-to-one chat, it SHOULD include the full JID (rather than the bare JID) in the invitation.

The invitations are delivered to the invitees:

When the client being used by <wiccarocks@shakespeare.lit/laptop> receives the invitation, it SHOULD auto-join the room or prompt the user whether to join (subject to user preferences) and then seamlessly convert the existing one-to-one chat window into a multi-user conferencing window:

Note: The fact that the messages come from the &ROOM; itself rather than &ROOMJID; is a clue to the receiving client that these messages are prior chat history, since any message from a room occupant will have a 'from' address equal to the sender's room JID.

If allowed in accordance with room configuration, a mere occupant MAY be allowed to change the subject in a room. For details, see the Modifying the Room Subject section of this document.

Since each occupant has a unique room JID, an occupant MAY send a "private message" to a selected occupant via the service by sending a message to the occupant's room JID. The message type SHOULD be "chat" and MUST NOT be "groupchat", but MAY be left unspecified (i.e., a normal message). This privilege SHOULD be allowed to any occupant (even a visitor in a moderated room).

The service is responsible for changing the 'from' address to the sender's room JID and delivering the message to the intended recipient's full JID.

If the sender attempts to send a private message of type "groupchat" to a particular occupant, the service MUST refuse to deliver the message (since the recipient's client would expect in-room messages to be of type "groupchat") and return a &badrequest; error to the sender:

If the sender attempts to send a private message to a room JID that does not exist, the service MUST return an ¬found; error to the sender.

If the sender is not an occupant of the room in which the intended recipient is visiting, the service MUST return a ¬acceptable; error to the sender.

An occupant sends a message to all other occupants in the room by sending a message of type "groupchat" to the &ROOM; itself (a service MAY ignore or reject messages that do not have a type of "groupchat"). In a moderated room, this privilege is restricted to occupants with a role of participant or higher.

If the sender has voice in the room (this is the default except in moderated rooms), the service MUST change the 'from' attribute to the sender's room JID and reflect the message out to the full JID of each occupant.

If the sender is a visitor (i.e., does not have voice in a moderated room), the service MAY return a &forbidden; error to the sender and MUST NOT reflect the message to all occupants. If the sender is not an occupant of the room, the service SHOULD return a ¬acceptable; error to the sender and SHOULD NOT reflect the message to all occupants; the only exception to this rule is that an implementation MAY allow users with certain privileges (e.g., a room owner, room admin, or service-level admin) to send messages to the room even if those users are not occupants.

An implementation MAY allow an unaffiliated user (in a moderated room, normally a participant) to register with a room and thus become a member of the room (conversely, an implementation MAY restrict this privilege and allow only room admins to add new members). In particular, it is not possible to join a members-only room without being on the member list, so an entity may need to request membership in order to join such a room.

If allowed, this functionality SHOULD be implemented by enabling a user to send a request for registration requirements to the room qualified by the 'jabber:iq:register' namespace as described in &xep0077;:

If the user requesting registration requirements is not allowed to register with the room (e.g., because that privilege has been restricted), the room MUST return a ¬allowed; error to the user. If the user is already registered, the room MUST reply with an IQ stanza of type "result" that contains an empty <register/> element as described in XEP-0077. If the room does not exist, the service MUST return an ¬found; error.

Otherwise, the room MUST then return a Data Form to the user (as described in &xep0004;). The information required to register MAY vary by implementation or deployment and is not fully specified in this document (e.g., the fields registered by this document for the 'http://jabber.org/protocol/muc#register' FORM_TYPE may be supplemented in the future via the mechanisms described in the Field Standardization section of this document). The following can be taken as a fairly typical example:

The user SHOULD then submit the form:

If the desired room nickname is already reserved for that room, the room MUST return a &conflict; error to the user:

If the room or service does not support registration, it MUST return a &unavailable; error to the user:

If the user did not include a valid data form, the room MUST return a &badrequest; error to the user:

Otherwise, the room MUST inform the user that the registration request was successfully received:

After the user submits the form, the service MAY request that the submission be approved by a room admin/owner (see the Approving Registration Requests section of this document) or MAY immediately add the user to the member list by changing the user's affiliation from "none" to "member". If the service changes the user's affiliation and the user is in the room, it MUST send updated presence from this individual to all occupants, indicating the change in affiliation by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "member".

If a user has registered with a room, the room MAY choose to restrict the user to use of the registered nickname only in that room. If it does so, it SHOULD return a ¬acceptable; error to the user if the user attempts to join the room with a roomnick other than the user's registered roomnick (this enables a room to "lock down" roomnicks for consistent identification of occupants).

A user MAY have a reserved room nickname, for example through explicit room registration, database integration, or nickname "lockdown". A user SHOULD discover his or her reserved nickname before attempting to enter the room. This is done by sending a Service Discovery information request to the room JID while specifying a well-known Service Discovery node of "x-roomuser-item".

It is OPTIONAL for a multi-user chat service to support the foregoing service discovery node. If the room or service does not support the foregoing service discovery node, it MUST return a &feature; error to the user. If it does and the user has a registered nickname, it MUST return the nickname to the user as the value of the 'name' attribute of a Service Discovery <identity/> element (for which the category/type SHOULD be "conference/text"):

If the user does not have a registered nickname, the room MUST return a service discovery &QUERY; element that is empty (in accordance with XEP-0030).

Even if a user has registered one room nickname, the service SHOULD allow the user to specify a different nickname on entering the room (e.g., in order to join from different client resources), although the service MAY choose to "lock down" nicknames and therefore deny entry to the user, including a ¬acceptable; error. The service MUST NOT return an error to the user if his or her client sends the foregoing request after having already joined the room, but instead SHOULD reply as described above.

If another user attempts to join the room with a nickname reserved by the first user, the service MUST deny entry to the second user and return a &conflict; error as previously described.

It is not possible for a visitor to speak (i.e., send a message to all occupants) in a moderated room. To request voice, a visitor SHOULD send a &MESSAGE; stanza containing a data form to the room itself, where data form contains only a 'muc#role' field with a value of "participant".

The service then SHOULD forward the request to the room moderator(s) as described in the Approving Voice Requests section of this document.

A common feature of multi-user chat rooms is the ability to change the subject within the room. By default, only users with a role of "moderator" SHOULD be allowed to change the subject in a room (although this SHOULD be configurable, with the result that a mere participant or even visitor may be allowed to change the subject if desired). The subject is changed by sending a message of type "groupchat" to the &ROOM;, containing no body but a <subject/> that specifies the new subject:

If a MUC service receives such a message, it MUST reflect the message to all other occupants with a 'from' address equal to the room JID that corresponds to the sender of the subject change:

In addition, the room SHOULD include the last subject change in the discussion history sent when a new occupant joins the room.

A MUC client that receives such a message MAY choose to display an in-room message, such as the following:

If someone without appropriate privileges attempts to change the room subject, the service MUST return a message of type "error" specifying a &forbidden; error condition:

A moderator has permissions kick certain kinds of occupants from a room (which occupants are "kickable" depends on service provisioning, room configuration, and the moderator's affiliation -- see below). The kick is normally performed based on the occupant's room nickname (though it MAY be based on the full JID) and is completed by setting the role of a participant or visitor to a value of "none".

The service MUST remove the kicked occupant by sending a presence stanza of type "unavailable" to each kicked occupant, including status code 307 in the extended presence information, optionally along with the reason (if provided) and the bare JID of the user who initiated the kick.

The inclusion of the status code assists clients in presenting their own notification messages (e.g., information appropriate to the user's locality). The optional inclusion of the reason and actor enable the kicked user to understand why he or she was kicked, and by whom if the kicked occupant would like to discuss the matter. Some commentors have complained that this opens room owners and administrators up to potential abuse; unfortunately, with great power comes great responsibility.

After removing the kicked occupant(s), the service MUST then inform the moderator of success:

After informing the moderator, the service MUST then inform all of the remaining occupants that the kicked occupant is no longer in the room by sending presence stanzas of type "unavailable" from the individual's roomnick (&ROOMJID;) to all the remaining occupants (just as it does when occupants exit the room of their own volition), including the status code and optionally the reason and actor.

A user cannot be kicked by a moderator with a lower affiliation. Therefore, if a moderator who is a participant attempts to kick an admin or a moderator who is a participant or admin attempts to kick an owner, the service MUST deny the request and return a ¬allowed; error to the sender:

If a moderator attempts to kick himself, the service MAY deny the request and return a &conflict; error to the sender. (Although the act of kicking oneself may seem odd, it is common in IRC as a way of apologizing for one's actions in the room.)

In a moderated room, a moderator may want to manage who does and does not have "voice" in the room (i.e., the ability to send messages to all occupants). Voice is granted based on the visitor's room nickname, which the service will convert into the visitor's full JID internally. The moderator grants voice to a visitor by changing the visitor's role to "participant" (the <reason/> element is optional):

The service MUST then inform the moderator of success:

The service MUST then send updated presence from this individual's &ROOMJID; to all occupants, indicating the addition of voice privileges by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'role' attribute set to a value of "participant".

In a moderated room, a moderator may want to revoke a participant's privileges to speak. The moderator can revoke voice from a participant by changing the participant's role to "visitor":

The service MUST then inform the moderator of success:

The service MUST then send updated presence from this individual to all occupants, indicating the removal of voice privileges by sending a presence element that contains an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'role' attribute set to a value of "visitor".

A moderator MUST NOT be able to revoke voice from a user whose affiliation is at or above the moderator's level. In addition, a service MUST NOT allow the voice privileges of an admin or owner to be removed by anyone. If a moderator attempts to revoke voice privileges from such a user, the service MUST deny the request and return a ¬allowed; error to the sender along with the offending item(s):

A moderator in a moderated room may want to modify the voice list. To do so, the moderator first requests the voice list by querying the room for all occupants with a role of 'participant'.

The service MUST then return the voice list to the moderator; each item MUST include the 'nick' and 'role' attributes and SHOULD include the 'affiliation' and 'jid' attributes:

The moderator MAY then modify the voice list. In order to do so, the moderator MUST send the changed items (i.e., only the "delta") back to the service; each item MUST include the 'nick' attribute and 'role' attribute (normally set to a value of "participant" or "visitor") but SHOULD NOT include the 'jid' attribute and MUST NOT include the 'affiliation' attribute (which is used to manage affiliations such as owner rather than the participant role):

The service MUST then inform the moderator of success:

The service MUST then send updated presence for any affected individuals to all occupants, indicating the change in voice privileges by sending the appropriate extended presence stanzas as described in the foregoing use cases.

As noted, voice privileges cannot be revoked from a room owner or room admin, nor from any user with a higher affiliation than the moderator making the request. If a room admin attempts to revoke voice privileges from such a user by modifying the voice list, the service MUST deny the request and return a ¬allowed; error to the sender:

As noted in the Requesting Voice section of this document, when a service receives a request for voice from an occupant it SHOULD forward that request to the room moderator(s). To do so, the service SHOULD send a &MESSAGE; stanza to the room moderator(s), where the &MESSAGE; stanza contains a data form asking for approval or denial of the request, as shown below.

In order to approve the request, a moderator shall submit the form:

If a moderator approves the voice request, the service shall grant voice to the occupant and send a presence update as described in the Granting Voice to a Visitor section of this document.

An admin or owner can ban one or more users from a room. The ban MUST be performed based on the occupant's bare JID. In order to ban a user, an admin MUST change the user's affiliation to "outcast".

The service MUST add that bare JID to the ban list, SHOULD remove the outcast's nickname from the list of registered nicknames, and MUST inform the admin or owner of success:

The service MUST also remove any banned users who are in the room by sending a presence stanza of type "unavailable" to each banned occupant, including status code 301 in the extended presence information, optionally along with the reason (if provided) and the bare JID of the user who initiated the ban.

The inclusion of the status code assists clients in presenting their own notification messages (e.g., information appropriate to the user's locality). The optional inclusion of the reason and actor enable the banned user to understand why he or she was banned, and by whom if the banned user would like to discuss the matter.

The service MUST then inform all of the remaining occupants that the banned user is no longer in the room by sending presence stanzas of type "unavailable" from the banned user to all remaining occupants (just as it does when occupants exit the room of their own volition), including the status code and optionally the reason and actor:

As with Kicking an Occupant, a user cannot be banned by an admin with a lower affiliation. Therefore, if an admin attempts to ban an owner, the service MUST deny the request and return a ¬allowed; error to the sender:

If an admin or owner attempts to ban himself, the service MUST deny the request and return a &conflict; error to the sender. (Note: This is different from the recommended service behavior on kicking oneself, which a service may allow.)

A room admin may want to modify the ban list. Note: The ban list is always based on a user's bare JID, although a nick (perhaps the last room nickname associated with that JID) MAY be included for convenience. To modify the list of banned JIDs, the admin first requests the ban list by querying the room for all users with an affiliation of 'outcast'.

The service MUST then return the list of banned users to the admin; each item MUST include the 'affiliation' and 'jid' attributes but SHOULD NOT include the 'nick' and 'role' attributes:

The admin MAY then modify the ban list. In order to do so, the admin MUST send the changed items (i.e., only the "delta") back to the service; each item MUST include the 'affiliation' attribute (normally set to a value of "outcast" to ban or "none" to remove ban) and 'jid' attribute but SHOULD NOT include the 'nick' attribute and MUST NOT include the 'role' attribute (which is used to manage roles such as participant rather than the outcast affiliation); in addition, the reason and actor elements are OPTIONAL:

After updating the ban list, the service MUST inform the admin of success:

The service MUST then remove the affected occupants (if they are in the room) and send updated presence (including the appropriate status code) from them to all the remaining occupants as described in the "Banning a User" use case. (The service SHOULD also remove each banned user's reserved nickname from the list of reserved roomnicks, if appropriate.)

When an entity is banned from a room, an implementation SHOULD match JIDs in the following order (these matching rules are the same as those defined for privacy lists in RFC 3921):

1. <user@domain/resource> (only that resource matches)
2. <user@domain> (any resource matches)
3. <domain/resource> (only that resource matches)
4. <domain> (the domain itself matches, as does any user@domain, domain/resource, or address containing a subdomain)

Some administrators may wish to ban all users associated with a specific domain from all rooms hosted by a MUC service. Such functionality is a service-level feature and is therefore out of scope for this document (but see &xep0133;).

An admin can grant membership to a user; this is done by changing the user's affiliation to "member" (normally based on nick if the user is in the room, or on bare JID if not; in either case, if the nick is provided, that nick becomes the user's default nick in the room if that functionality is supported by the implementation):

The service MUST add the user to the member list and then inform the admin of success:

If the user is in the room, the service MUST then send updated presence from this individual to all occupants, indicating the granting of membership by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "member".

An admin may want to revoke a user's membership; this is done by changing the user's affiliation to "none":

The service MUST remove the user from the member list and then inform the moderator of success:

The service MUST then send updated presence from this individual to all occupants, indicating the loss of membership by sending a presence element that contains an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "none".

If the room is members-only, the service MUST remove the user from the room, including a status code of 321 to indicate that the user was removed because of an affiliation change, and inform all remaining occupants:

In the context of a members-only room, the member list is essentially a "whitelist" of people who are allowed to enter the room. Anyone who is not a member is effectively banned from entering the room, even if their affiliation is not "outcast".

In the context of an open room, the member list is simply a list of users (bare JID and reserved nick) who are registered with the room. Such users may appear in a room roster, have their room nickname reserved, be returned in search results or FAQ queries, and the like.

It is RECOMMENDED that only room admins have the privilege to modify the member list in members-only rooms. To do so, the admin first requests the member list by querying the room for all users with an affiliation of "member":

(A service SHOULD also return the member list to any occupant in a members-only room; i.e., it SHOULD NOT generate a &forbidden; error when a member in the room requests the member list. This functionality may assist clients in showing all the existing members even if some of them are not in the room, e.g. to help a member determine if another user should be invited.)

The service MUST then return the full member list to the admin qualified by the 'http://jabber.org/protocol/muc#admin' namespace; each item MUST include the 'affiliation' and 'jid' attributes and MAY include the 'nick' and 'role' attributes for each members that is currently an occupant.

The admin MAY then modify the member list. In order to do so, the admin MUST send the changed items (i.e., only the "delta") to the service; each item MUST include the 'affiliation' attribute (normally set to a value of "member" or "none") and 'jid' attribute but SHOULD NOT include the 'nick' attribute and MUST NOT include the 'role' attribute (which is used to manage roles such as participant rather than the member affiliation):

The service MUST modify the member list and then inform the moderator of success:

The service MUST change the affiliation of any affected user. If the user has been removed from the member list, the service MUST change the user's affiliation from "member" to "none". If the user has been added to the member list, the service MUST change the user's affiliation to "member".

If a removed member is currently in a members-only room, the service SHOULD kick the occupant by changing the removed member's role to "none" and send appropriate presence to the removed member as previously described. No matter whether the removed member was in or out of a members-only room, the service MUST subsequently refuse entry to the user.

For all room types, the service MUST send updated presence from this individual to all occupants, indicating the change in affiliation by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "none".

In addition, the service SHOULD send an invitation to any user who has been added to the member list of a members-only room if the user is not currently affiliated with the room, for example as an admin or owner (such a user would by definition not be in the room; note also that this example includes a password but not a reason -- both child elements are OPTIONAL):

While only admins and owners SHOULD be allowed to modify the member list, an implementation MAY provide a configuration option that opens invitation privileges to any member of a members-only room. In such a situation, any invitation sent SHOULD automatically trigger the addition of the invitee to the member list. However, if invitation privileges are restricted to admins and a mere member attempts to a send an invitation, the service MUST deny the invitation request and return a &forbidden; error to the sender:

Invitations sent through an open room MUST NOT trigger the addition of the invitee to the member list.

If a user is added to the member list of an open room and the user is in the room, the service MUST send updated presence from this individual to all occupants, indicating the change in affiliation by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "member".

An admin may want to grant moderator privileges to a participant or visitor; this is done by changing the user's role to "moderator":

The service MUST add the user to the moderator list and then inform the admin of success:

The service MUST then send updated presence from this individual to all occupants, indicating the addition of moderator privileges by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'role' attribute set to a value of "moderator".

An admin may want to revoke a user's moderator privileges. An admin MAY revoke moderator privileges only from a user whose affiliation is "member" or "none" (i.e., not from an owner or admin). The privilege is revoked by changing the user's role to "participant":

The service MUST remove the user from the moderator list and then inform the admin of success:

The service MUST then send updated presence from this individual to all occupants, indicating the removal of moderator privileges by sending a presence element that contains an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'role' attribute set to a value of "participant".

As noted, an admin MUST NOT be allowed to revoke moderator privileges from a user whose affiliation is "owner" or "admin". If an admin attempts to revoke moderator privileges from such a user, the service MUST deny the request and return a ¬allowed; error to the sender:

An admin may want to modify the moderator list. To do so, the admin first requests the moderator list by querying the room for all users with a role of 'moderator'.

The service MUST then return the moderator list to the admin; each item MUST include the 'jid', 'nick', and 'role' attributes and SHOULD include the 'affiliation' attribute:

The admin MAY then modify the moderator list. In order to do so, the admin MUST send the changed items (i.e., only the "delta") back to the service; each item MUST include the 'jid' attribute and 'role' attribute (normally set to a value of "member" or "participant") but SHOULD NOT include the 'nick' attribute and MUST NOT include the 'affiliation' attribute (which is used to manage affiliations such as admin rather than the moderator role):

The service MUST modify the moderator list and then inform the admin of success:

The service MUST then send updated presence for any affected individuals to all occupants, indicating the change in moderator privileges by sending the appropriate extended presence stanzas as described in the foregoing use cases.

As noted, moderator privileges cannot be revoked from a room owner or room admin. If a room admin attempts to revoke moderator privileges from such a user by modifying the moderator list, the service MUST deny the request and return a ¬allowed; error to the sender:

If a service does not automatically accept requests to register with a room, it MAY provide a way for room admins to approve or deny registration requests over Jabber (alternatively, it could provide a web interface or some other admin tool). The simplest way to do so is for the service to send a &MESSAGE; stanza to the room admin(s) when the registration request is received, where the &MESSAGE; stanza contains a Data Form asking for approval or denial of the request. The following Data Form is RECOMMENDED but implementations MAY use a different form entirely, or supplement the following form with additional fields.

If the admin approves the registration request, the service shall register the user with the room.

More advanced registration approval mechanisms (e.g., retrieving a list of registration requests using &xep0050; as is done in &xep0060;) are out of scope for this document.

At any time after specifying the initial configuration of the room, a room owner may want to change the configuration. In order to initiate this process, a room owner MUST request a new configuration form from the room by sending an IQ to &ROOM; containing an empty <query/> element qualified by the 'http://jabber.org/protocol/muc#owner' namespace.

If the <user@host> of the 'from' address does not match the bare JID of a room owner, the service MUST return a &forbidden; error to the sender:

Otherwise, the service MUST send a configuration form to the room owner with the current options set as defaults:

If there are no configuration options available, the service MUST return an empty query element to the room owner as shown in the previous use case.

The room owner SHOULD then submit the form with updated configuration information.

Alternatively, the room owner MAY cancel the configuration process:

If the room owner cancels the subsequent configuration, the service MUST leave the configuration of the room as it was before the room owner initiated the subsequent configuration process.

If as a result of a change in the room configuration a room admin loses administrative privileges while the admin is in the room, the room MUST send updated presence for that individual to all occupants, denoting the change in status by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "member" and the 'role' attribute set to a value of "participant" or "visitor" as appropriate for the affiliation level and the room type:

If as a result of a change in the room configuration a user gains administrative privileges while the user is in the room, the room MUST send updated presence for that individual to all occupants, denoting the change in status by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "admin" and the 'role' attribute set to a value of "admin":

If as a result of a change in the room configuration a room owner loses owner privileges while that owner is in the room, the room MUST send updated presence for that individual to all occupants, denoting the change in status by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "admin" and the 'role' attribute set to an appropriate value given the affiliation and room type ("moderator" is recommended).

A service MUST NOT allow an owner to revoke his or her own ownership privileges if there are no other owners; if an owner attempts to do this, the service MUST return a &conflict; error to the owner. However, a service SHOULD allow an owner to revoke his or her own ownership privileges if there are other owners.

If as a result of a change in the room configuration a user gains ownership privileges while the user is in the room, the room MUST send updated presence for that individual to all occupants, denoting the change in status by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "owner" and the 'role' attribute set to an appropriate value given the affiliation and room type ("moderator" is recommended).

If as a result of a change in the room configuration the room type is changed to members-only but there are non-members in the room, the service MUST remove any non-members from the room and include a status code of 322 in the presence unavailable stanzas sent to those users as well as any remaining occupants.

If allowed by an implementation, an owner MAY grant ownership privileges to another user; this is done by changing the user's affiliation to "owner":

The service MUST add the user to the owner list and then inform the owner of success:

If the user is in the room, the service MUST then send updated presence from this individual to all occupants, indicating the granting of ownership privileges by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "owner" and the 'role' attribute set to an appropriate value given the affiliation and room type ("moderator" is recommended).

An implementation MAY allow an owner to revoke another user's ownership privileges; this is done by changing the user's affiliation to something other than "owner":

A service MUST NOT allow an owner to revoke his or her own ownership privileges if there are no other owners; if an owner attempts to do this, the service MUST return a &conflict; error to the owner. However, a service SHOULD allow an owner to revoke his or her own ownership privileges if there are other owners.

If an implementation does not allow one owner to revoke another user's ownership privileges, the implementation MUST return a ¬authorized; error to the owner who made the request.

In all other cases, the service MUST remove the user from the owner list and then inform the owner of success:

If the user is in the room, the service MUST then send updated presence from this individual to all occupants, indicating the loss of ownership privileges by sending a presence element that contains an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value other than "owner" and the 'role' attribute set to an appropriate value:

Note: Allowing an owner to remove another user's ownership privileges can compromise the control model for room management; therefore this feature is OPTIONAL, and implementations are encouraged to support owner removal through an interface that is open only to individuals with service-wide administrative privileges.

If allowed by an implementation, a room owner may want to modify the owner list. To do so, the owner first requests the owner list by querying the room for all users with an affiliation of 'owner'.

If the <user@host> of the 'from' address does not match the bare JID of a room owner, the service MUST return a &forbidden; error to the sender.

Otherwise, the service MUST then return the owner list to the owner; each item MUST include the 'affiliation' and 'jid' attributes and MAY include the 'nick' and 'role' attributes for any owner that is currently an occupant:

The owner MAY then modify the owner list. In order to do so, the owner MUST send the changed items (i.e., only the "delta") back to the service; This is different from the behavior of room configuration, wherein the 'muc#roomconfig_roomowners' field specifies the full list of room owners, not the delta. each item MUST include the 'affiliation' and 'jid' attributes but SHOULD NOT include the 'nick' attribute and MUST NOT include the 'role' attribute (which is used to manage roles such as participant rather than the owner affiliation):

Only owners shall be allowed to modify the owner list. If a non-owner attempts to view or modify the owner list, the service MUST deny the request and return a &forbidden; error to the sender:

A service MUST NOT allow an owner to revoke his or her own ownership privileges if there are no other owners; if an owner attempts to do this, the service MUST return a &conflict; error to the owner. However, a service SHOULD allow an owner to revoke his or her own ownership privileges if there are other owners.

In all other cases, the service MUST modify owner list and then inform the owner of success:

The service MUST also send presence notifications related to any affiliation changes that result from modifying the owner list as previously described.

An owner can grant administrative privileges to a member or unaffiliated user; this is done by changing the user's affiliation to "admin":

The service MUST add the user to the admin list and then inform the owner of success:

If the user is in the room, the service MUST then send updated presence from this individual to all occupants, indicating the granting of administrative privileges by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "admin" and the 'role' attribute set to an appropriate value given the affiliation and room type.

An owner may want to revoke a user's administrative privileges; this is done by changing the user's affiliation to something other than "admin" or "owner":

The service MUST remove the user from the admin list and then inform the owner of success:

The service MUST then send updated presence from this individual to all occupants, indicating the loss of administrative privileges by sending a presence element that contains an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value other than "admin" or "owner" and the 'role' attribute set to an appropriate value given the affiliation level and the room type:

A room owner may want to modify the admin list. To do so, the owner first requests the admin list by querying the room for all users with an affiliation of 'admin'.

If the <user@host> of the 'from' address does not match the bare JID of a room owner, the service MUST return a &forbidden; error to the sender.

Otherwise, the service MUST then return the admin list to the owner; each item MUST include the 'affiliation' and 'jid' attributes and MAY include the 'nick' and 'role' attributes for any admin that is currently an occupant:

The owner MAY then modify the admin list. In order to do so, the owner MUST send the changed items (i.e., only the "delta") back to the service; This is different from the behavior of room configuration, wherein the 'muc#roomconfig_roomadmins' field specifies the full list of room admins, not the delta. each item MUST include the 'affiliation' attribute (normally set to a value of "admin" or "none") and 'jid' attribute but SHOULD NOT include the 'nick' attribute and MUST NOT include the 'role' attribute (which is used to manage roles such as participant rather than the admin affiliation):

Only owners shall be allowed to modify the admin list. If a non-owner attempts to view or modify the admin list, the service MUST deny the request and return a &forbidden; error to the sender:

Otherwise, the service MUST modify the admin list and then inform the owner of success:

The service MUST also send presence notifications related to any affiliation changes that result from modifying the admin list as previously described.

A room owner MUST be able to destroy a room, especially if the room is persistent. The workflow is as follows:

1. The room owner requests that the room be destroyed, specifying a reason and an alternate venue if desired.

2. The room removes all users from the room (including appropriate information about the alternate location and the reason for being removed) and destroys the room, even if it was defined as persistent.

Other than the foregoing, this document does not specify what (if anything) a MUC service implementation shall do as a result of a room destruction request. For example, if the room was defined as persistent, an implementation MAY choose to lock the room ID so that it cannot be re-used, redirect enter requests to the alternate venue, or invite the current participants to the new room; however, such behavior is OPTIONAL.

In order to destroy a room, the room owner MUST send an IQ set to the address of the room to be destroyed. The &IQ; stanza shall contain a &QUERY; element qualified by the 'http://jabber.org/protocol/muc#owner' namespace, which in turn shall contain a <destroy/> element. The address of the alternate venue MAY be provided as the value of the <destroy/> element's 'jid' attribute. A password for the alternate venue MAY be provided as the XML character data of a <password/> child element of the <destroy/> element. The reason for the room destruction MAY be provided as the XML character data of a <reason/> child element of the <destroy/> element.

The following examples illustrate the protocol elements to be sent and received:

The service is responsible for removing all the occupants. It SHOULD NOT broadcast presence stanzas of type "unavailable" from all occupants, instead sending only one presence stanza of type "unavailable" to each occupant so that the user knows he or she has been removed from the room. If extended presence information specifying the JID of an alternate location and the reason for the room destruction was provided by the room owner, the presence stanza MUST include that information.

If the <user@host> of the 'from' address received on a destroy request does not match the bare JID of a room owner, the service MUST return a &forbidden; error to the sender:

The error codes associated with the 'http://jabber.org/protocol/muc#user' namespace are fairly straightforward, as summarized in the following table. For detailed information about mapping legacy error codes to XMPP-style error types and conditions, refer to &xep0086;; implementations SHOULD support both legacy and XMPP error handling.

This document does not stipulate text strings (i.e., values of the XMPP <text/> element) associated with the foregoing error conditions.

Multi-User Chat uses a <status/> element (specifically, the 'code' attribute of the <status/> element) to communicate information about a user's status in a room. Over time, the number of status codes has grown quite large, and new status codes continue to be requested of the author. Therefore, these codes are now documented in a registry maintained by the XMPP Registrar. For details, refer to the Status Codes Registry section of this document.

Note: In general, MUC status codes tend to follow the "philosophy" of status codes that is implicit in &rfc2616; and &rfc1893; (1xx codes are informational, 2xx codes specify that it is fine to continue, 3xx codes specify redirects such as being kicked or banned, x3x codes refer to system status, x7x codes refer to security or policy matters, etc.).

Note: If the MUC protocol were being designed today, it would specify a more flexible, XML-friendly approach rather than hardcoded status numbers; however, at this point the pain of changing the status reporting system would be greater than the benefit of doing so, which is why the status code numbers remain in use. A future version of this document may define a more XMPP-like approach to status conditions, retaining the code numbers but supplementing them with more descriptive child elements as is done in RFC 3920.

No room entrance authentication or authorization method more secure than cleartext passwords is defined or required by this document. However, the risks involved can mitigated by the use of channel encryption and strong authentication via TLS and SASL as described in RFC 3920.

No end-to-end message or session encryption method is specified herein. Users SHOULD NOT trust a service to keep secret any text sent through a room.

Depending on room configuration, a room may publicly log all discussions held in the room. A service MUST warn the user that the room is publicly logged by returning a status code of "170" with the user's initial presence, and user's the client MUST so warn the user if the room discussion is logged (a user's client SHOULD also query the room for its configuration prior to allowing the user to enter in order to "pre-discover" whether the room is logged). A client MUST also warn the user if the room's configuration is subsequently modified to allow room logging (which the client will discover when the room sends status code 170). Note: In-room history is different from public room logging, and naturally a room cannot effectively prevent occupants from separately maintaining their own room logs, which may become public; users SHOULD exercise due caution and consider any room discussions to be effectively public.

Depending on room configuration, a room MAY expose each occupant's real JID to other occupants (if the room is non-anonymous) and will almost certainly expose each occupant's real JID to the room owners and administrators (if the room is not fully-anonymous). A service MUST warn the user that real JIDs are exposed in the room by returning a status code of "100" with the user's initial presence, and the user's client MUST so warn the user (a user's client SHOULD also query the room for its configuration prior to allowing the user to enter in order to "pre-discover" whether real JIDs are exposed in the room). A client MUST also warn the user if the room's configuration is subsequently modified from semi-anonymous or fully-anonymous to non-anonymous (which the client will discover when the room sends status code 172) and SHOULD warn the user if the room's configuration is subsequently modified from fully-anonymous to semi-anonymous (which the client will discover when the room sends status code 173).

The XMPP Registrar includes the following MUC-related namespaces in its registry of protocol namespaces:

• http://jabber.org/protocol/muc
• http://jabber.org/protocol/muc#admin
• http://jabber.org/protocol/muc#owner
• http://jabber.org/protocol/muc#unique
• http://jabber.org/protocol/muc#user

A Multi-User Chat service or room is identified by the "conference" category and the "text" type within Service Discovery.

There are many features related to a MUC service or room that can be discovered by means of Service Discovery. The most fundamental of these is the 'http://jabber.org/protocol/muc' namespace. In addition, a MUC room SHOULD provide information about the specific room features it implements, such as password protection and room moderation.

The well-known Service Discovery node 'http://jabber.org/protocol/muc#rooms' enables discovery of the rooms in which a user is an occupant.

The well-known Service Discovery node 'x-roomuser-item' enables a user to discover his or her registered roomnick from outside the room.

The well-known Service Discovery node 'http://jabber.org/protocol/muc#traffic' enables discovery of the namespaces that are allowed in traffic sent through a room (see the Allowable Traffic section of this document).

&xep0068; defines a process for standardizing the fields used within Data Forms qualified by a particular namespace. Within MUC, there are four uses of such forms: room registration (the "muc#register" FORM_TYPE), requesting voice and approving voice requests ("muc#request"), room configuration ("muc#roomconfig"), and service discovery extensions for room information ("muc#roominfo"). The reserved fields are defined below.

As authorized by &xep0147;, the XMPP Registrar maintains a registry of queries and key-value pairs for use in XMPP URIs (see &QUERYTYPES;).

In order to provide consistency regarding the addresses captured in room JIDs, Room IDs MUST match the Nodeprep profile of Stringprep and Room Nicknames MUST match the Resourceprep profile of Stringprep (both of these are defined in RFC 3920). Although not explicitly stated in RFC 3920, both the Room ID (node) and Room Nickname (resource) portions of a Room JID MUST be of non-zero length. In addition, a MUC service MUST NOT allow empty or invisible Room Nicknames (i.e., Room Nicknames that consist only of one or more space characters).

1. If an occupant wants to send a message to all other occupants, a MUC client MUST set the 'type' attribute to a value of "groupchat". A service MAY ignore messages that are improperly typed, or reject them with a &badrequest; error.

2. If a MUC service receives a message directed to the room or to a single occupant from a Jabber user who has a role of "none", the service MUST NOT deliver the message and SHOULD return the message to the sender with a &forbidden; error.

3. If a MUC service receives a message directed to a room that does not exist or is not yet unlocked, the service SHOULD return the message to the sender with an ¬found; error.

4. A MUC service SHOULD pass extended information (e.g., an XHTML version of the message body) through to occupants unchanged; however, a MUC service MAY disallow message specific extensions (see the Allowable Traffic section of this document).

5. A MUC client MAY generate extensions that conform to the &xep0022; or &xep0085; specification; however, a MUC service MAY disallow these extensions (see the Allowable Traffic section of this document).

1. A room MUST silently ignore unavailable presence received from a user who has a role of "none".

2. Only the MUC service itself SHOULD generate extended presence information about roles, affiliations, full JIDs, or status codes qualified by the 'http://jabber.org/protocol/muc#user' namespace (based on information the service knows about occupants, e.g., roles, or as a result of actions taken by a moderator or room administrator). A client SHOULD NOT presume to generate such information. If a MUC service receives such extended presence information from an occupant, it MUST NOT reflect it to other occupants. (A client MAY generate extended presence information qualified by the 'http://jabber.org/protocol/muc#user' namespace in order to supply a password, but naturally this is not reflected to other occupants.)

3. A MUC service SHOULD allow all other presence information to pass through, although it MAY choose to block extended presence information; see the Allowable Traffic section of this document.

4. In order to appropriately inform occupants of room roles and affiliations, and to make it easier for Jabber clients to track the current state of all users in the room, MUC service implementations MUST provide extended presence information about roles and affiliations in all presence stanzas, including presence stanzas of type "unavailable" sent when a user exits the room for any reason.

5. If a privilege is revoked, the service MUST note that by sending an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child element with the 'role' and/or 'affiliation' attributes set to a value that indicates the loss of the relevant privilege. All future presence stanzas for the occupant MUST include the updated role and affiliation, until and unless they change again.

6. A MUC service MUST send extended presence to a client even if the client did not send an empty <x/> element qualified by the 'http://jabber.org/protocol/muc' namespace on entering the room; naturally, a client MUST ignore such information if it does not understand it (in accordance with RFC 3920).

7. Extended presence about roles and affiliations sent in the muc#user namespace MUST include the full JID (not the bare JID) as the value of the 'jid' attribute.

8. A client MAY send a custom exit message if desired (as is often done in IRC channels) by including a <status/> element in the presence stanza of type "unavailable" sent when exiting a room.

1. If an occupant wants to send an IQ stanza to another user in a non-anonymous room, the sender SHOULD send the request directly to the recipient's bare JID or full JID, rather than attempting to send the request through the room (i.e., via the recipient's room JID).

2. If an occupant wants to send an IQ stanza to another user in a semi-anonymous room, the sender can direct the stanza to the recipient's room JID and the service MAY forward the stanza to the recipient's real JID. However, a MUC service MUST NOT reveal the sender's real JID to the recipient at any time, nor reveal the recipient's real JID to the sender.

3. A MUC client MUST send only the 'affiliation' attribute or the 'role' attribute in the <item/> element contained within an IQ set qualified by the 'http://jabber.org/protocol/muc#admin' namespace; if a moderator, admin, or owner attempts to modify both the affiliation and role of the same item in the same IQ set, the service MUST return a &badrequest; error to the sender. However, a MUC service MAY modify a role based on a change to an affiliation and thus MAY send presence updates that include both a modified role and a modified affiliation.

4. In IQ sets regarding roles, a MUC client MUST include the 'nick' attribute only; in IQ results regarding roles, a MUC service MUST include the 'nick', 'role', 'affiliation', and 'jid' attributes (with the value of the latter set to the user's full JID).

5. In IQ sets regarding affiliations, a MUC client MUST include the 'jid' attribute only (with the value set to the bare JID); in IQ results regarding affiliations, a MUC service MUST NOT include the 'role' attribute, MUST include the 'affiliation' attribute and the 'jid' attribute (with the value set to the bare JID), and SHOULD include the 'nick' attribute (except if the affiliation is "outcast", since outcasts SHOULD NOT have reserved nicknames).

1. In handling messages sent by visitors in a moderated room, a MUC service MAY queue each message for approval by a moderator and MAY inform the sender that the message is being held for approval; however, such behavior is OPTIONAL, and definition of a message approval protocol (e.g., using Data Forms as defined in XEP-0004) is out of scope for this document.

2. It is common for MUC services to provide in-room messages when certain events occur, such as when the subject changes, when an occupant enters or exits, or when a room is destroyed. Such messages are entirely OPTIONAL and are left up to the implementation or deployment, but if used MUST be messages of type "groupchat" sent from the room JID itself (&ROOM;) rather than a specific occupant (&ROOMJID;). However, in general it is preferable for the receiving client to generate such messages based on events in the room (e.g., user entrances and exits) as well as specific status codes provided in MUC; this will help ensure correct localization of such messages.

3. Out of courtesy, a MUC service MAY send an out-of-room <message/> to an occupant who is kicked or banned, and MAY broadcast an in-room <message/> to all remaining occupants informing them that the occupant has been kicked or banned from the room. However, such messages are OPTIONAL, and indeed are unnecessary since the information required for a receiving client to generate such messages is communicated in the presence stanzas (specifically the status codes) sent by a MUC service.

4. Out of courtesy, a MUC service MAY send an out-of-room <message/> if a user's affiliation changes while the user is not in the room; the message SHOULD be sent from the room to the user's bare JID, MAY contain a <body/> element describing the affiliation change, and MUST contain a status code of 101.

5. There is no requirement that a MUC service shall provide special treatment for users of the older "groupchat 1.0" protocol, such as messages that contain equivalents to the extended presence information that is qualified by the 'http://jabber.org/protocol/muc#user' namespace.

6. Room types MAY be configured in any combination. A MUC service MAY support or allow any desired room types or combinations thereof.

7. A MUC service MAY limit the number of configuration options presented to an owner after initial configuration has been completed, e.g. because certain options cannot take effect without restarting the service.

8. A MUC service MAY provide an interface to room creation and configuration (e.g., in the form of a special Jabber user or a Web page), so that the ostensible room owner is actually the application instead of a human user.

9. A MUC service MAY choose to make available a special in-room resource that provides an interface to administrative functionality (e.g., a "user" named "ChatBot"), which occupants could interact with directly, thus enabling admins to type '/command parameter' in a private message to that "user". Obviously this kind of implementation would require the service to add a 'ChatBot' user to the room when it is created, and to prevent any occupant from having the nickname 'ChatBot' in the room. This might be difficult to ensure in some implementations or deployments. In any case, any such interface is OPTIONAL.

10. A MUC service SHOULD remove a user if the service receives a delivery-related error in relation to a stanza it has previously sent to the user (remote server unreachable, user not found, etc.).

11. A MUC service MAY choose to discard extended presence information that is attached to a &PRESENCE; stanza before reflecting the presence change to the occupants of a room. That is, an implementation MAY choose to reflect only the <show/>, <status/>, and <priority/> child elements of the presence element as specified in the XML schema for the 'jabber:client' namespace, with the result that presence "changes" in extended namespaces (e.g., gabber:x:music:info) are not passed through to occupants. If a service prohibits certain extended namespaces, it SHOULD provide a description of allowable traffic at the well-known Service Discovery node 'http://jabber.org/protocol/muc#traffic' as described in the Allowable Traffic section of this document.

12. A MUC service MAY choose to discard extended information attached to &MESSAGE; stanzas before reflecting the message to the occupants of a room. An example of such extended information is the lightweight text markup specified by &xep0071;. If a service prohibits certain extended namespaces, it SHOULD provide a description of allowable traffic at the well-known Service Discovery node 'http://jabber.org/protocol/muc#traffic' as described in the Allowable Traffic section of this document.

13. A MUC service MAY choose to "lock down" room nicknames (e.g., hardcoding the room nickname to the bare JID of the occupant). If so, the service MUST treat the locked down nickname as a reserved room nickname and MUST support the protocol specified in the Discovering Reserved Room Nickname section of this document.

1. Jabber clients MAY present room roles by showing ad-hoc groups for each role within a room roster. This will enable occupants to clearly visualize which occupants are moderators, participants, and visitors. However, such a representation is OPTIONAL.

2. Jabber clients MAY implement a variety of interface styles that provide "shortcuts" to functionality such as changing one's nickname, kicking or banning users, discovering an occupant's full JID, or changing the subject. One option consists of IRC-style commands such as '/nick', '/kick', '/ban', and '/whois'; another is to enable a user to right-click items in a room roster. All such interface styles are OPTIONAL. However, for convenience, a mapping of IRC commands to MUC protocols is provided below.