HTML 4.0  defines a <link/> element that defines a relationship between a document and another resource on the Internet. Such a resource can be a JabberID. Examples include the JabberID of a document author, a Multi-User Chat (XEP-0045)  room where the document can be discussed, or a Publish-Subscribe (XEP-0060)  node where RSS or Atom feeds related to the document are hosted (e.g., see RFC 4287 ). This specification defines a recommended approach for linking to JabberIDs in this way.
The RECOMMENDED format is as follows.
The 'href' attribute is REQUIRED and its value MUST be an XMPP URI or IRI that conforms to RFC 5122 . The URI SHOULD NOT include an action as described in XMPP URI Query Components (XEP-0147)  and registered at <https://xmpp.org/registrar/querytypes.html>, so that the URI can be appropriately dereferenced as described below. The URI MAY include a node key as shown in the examples below.
The 'rel' attribute is RECOMMENED and its value SHOULD be a link relation as registered in the IANA MIME Atom Link Relations Registry  or other registry.
In addition to 'href' and 'rel', the HTML and XHTML specifications define a number of other allowable attributes for the <link/> element. These attributes MAY be included. However, because a JabberID is a bare address and there is no hosted media associated with a JabberID, the 'charset', 'media', and 'type' attribute SHOULD NOT be included.
When an application encounters an auto-discovery link to a JabberID, it SHOULD pass it to an appropriate helper application (such as an XMPP client). The helper application then SHOULD dereference the URI, and send an XMPP Service Discovery (XEP-0030)  request to the referenced JID, passing the optional node parameter. The service discovery response therefore enables a full range of future actions.
The following example shows a JabberID that points to the same entity as the document itself (e.g., the author of an "about-the-author" page).
The following example shows a JabberID that points to a multi-user chat room where the document can be discussed.
The following example shows a JabberID that points to a publish-subscribe node where notifications related to the document can be retrieved.
Advertising an XMPP address so that it can be automatically discovered may expose that address to abusive communications. Care should be taken when choosing whether to advertise a JID that corresponds to an end user's primary XMPP address.
This document currently requires no interaction with the Internet Assigned Numbers Authority (IANA) . However, a future version of this specification may register new link relations with the IANA.
This document requires no interaction with the XMPP Registrar .
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This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).
The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <firstname.lastname@example.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <email@example.com>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
7. IANA registry of Atom link relations <http://www.iana.org/assignments/link-relations.html>.
9. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
10. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/