The user's XMPP server might have special information that enables it to flag a resource as primary for a given application type. For instance, the server may include a communication policy service that enables the user to define (outside the context of any presence priorities) that she would prefer to be called at her desktop computer only between the hours of 9:00 AM and 5:00 PM local time, prefer to be called on her mobile phone at all other times, and so on.

To flag the primary resource related to a specific application type, the server shall add a <primary/> child to the relevant RAP element. Here is an example:

The following business rules apply to primary resource flagging by the server:

1. A server MAY add the <primary/> element to RAP data generated by the resource it determines is "most available" for a given application type.

2. Because the default 'ns' is "jabber:client", to flag the primary resource for standard XMPP communications the server SHOULD NOT include a 'ns' attribute, SHOULD NOT include a 'num' attribute, and MUST include a <primary/> child.

3. An available resource that has specified a negative priority for an application type MUST NOT be flagged as the primary resource for that application type.

4. A client SHOULD NOT include the <primary/> element in RAP data that it generates; however, if a client includes a <primary/> element, the server SHOULD remove or overwrite the element.

5. In response to a presence probe, a server SHOULD send presence from the primary resource first (this enables the receiving client to skip any local "most-available-resource" algorithms it might implement) if the client includes RAP data in presence.

6. If the primary resource changes for a given application type and the client includes RAP data in presence, a server MUST broadcast updated presence information (including the <primary/> element) for the new primary resource. If the change in primary resource occurs because of a presence broadcast from the current primary resource, the server MUST push presence from the current primary resource (without the <primary/> element) before pushing presence from the new primary resource (including the <primary/> element).

A server MAY use the RAP data provided by a client in determining how to route incoming &MESSAGE; stanzas directed to the bare JID &LOCALBARE; of a registered account. In order to enable such routing, the sender MUST include an empty <route/> element qualified by the 'urn:xmpp:raproute:0' namespace &VNOTE; including an 'ns' attribute corresponding to the desired application type.

For example, consider a &xep0155; request sent from one user (Romeo) to another (Juliet), where the users do not share presence. Romeo wants the request to be delivered to the highest-priority resource for the "urn:xmpp:jingle:apps:rtp:0" application type.

If Juliet's server supports RAP routing, it would then deliver the message to whichever of Juliet's resources has the highest priority for the "urn:xmpp:jingle:apps:rtp:0" application type.

If an entity supports resource application priorities, it MUST advertise that fact by returning a feature of "urn:xmpp:rap:0", "urn:xmpp:raproute:0", or both &VNOTE; in response to &xep0030; information requests.

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

When the pubsub transport is used, client publishing of resource application priority can result in a presence leak if the node access model is "open". Care should be taken in properly configuring the pubsub node so that unauthorized entities are not able to retrieve information about the user's available resources.

Server flagging of the primary resource is not known to introduce any vulnerabilities or compromises of user privacy.

This document requires no interaction with &IANA;.