The 'jabber:iq:private' namespace has previously been documented in the Jabber Programmers Guide, but not in a canonical form such as the Internet-Drafts or a XEP. This specification documents the existing usage of jabber:iq:private.
A Jabber client can store any arbitrary XML on the server side by sending an <iq/> stanza of type "set" to the server with a <query/> child scoped by the 'jabber:iq:private' namespace. The <query/> element MAY contain any arbitrary XML fragment as long as the root element of that fragment is scoped by its own namespace. The data can then be retrieved by sending an <iq/> stanza of type "get" with a <query/> child scoped by the 'jabber:iq:private' namespace, which in turn contains a child element scoped by the namespace used for storage of that fragment. Using this method, Jabber entities can store private data on the server and retrieve it whenever necessary. The data stored might be anything, as long as it is valid XML. One typical usage for this namespace is the server-side storage of client-specific preferences; another is Bookmark Storage (XEP-0048) .
|get||Sent with a blank query to retrieve the private data from the server.|
|set||Sent with the private XML data contained inside of a query.|
|result||Returns the private data from the server.|
|error||There was an error processing the request. The exact error can be found in the child error element.|
The root element of this namespace is query. At least one child element with a proper namespace MUST be included; otherwise the server MUST respond with a "Not Acceptable" error (see Error Condition Mappings (XEP-0086)  for information about error conditions). A client MUST NOT query for more than one namespace in a single IQ get request. However, an IQ set or result MAY contain multiple elements qualified by the same namespace.
If a user attempts to get or set jabber:iq:private data that belongs to another user, the server MUST return a "Forbidden" or "Service Unavailable" error to the sender (the latter condition is in common use by existing implementations, although the former is preferable).
If a user attempts to perform an IQ get without providing a child element, the server SHOULD return a "Bad Format" error (however, some existing implementations return a "Not Acceptable" error in such circumstances):
Certain namespaces are reserved in Jabber (namespaces beginning with 'jabber:' or 'http://jabber.org/', as well as 'vcard-temp'). If a user attempts to get or set jabber:iq:private data in a reserved namespace, historically some server implementations have chosen to return an error (commonly "Not Acceptable") to the sender. Such behavior is OPTIONAL, but may be encountered by clients when interacting with some existing server implementations.
|Bad Format||The IQ get does not contain a child element.|
|Forbidden||The IQ get or set is sent to a JID other than that of the sender.|
|Not Acceptable||The IQ get or set is qualified by a reserved namespace.|
A server MUST NOT allow any entity other than an authorized resource of the user to create, update, or delete private XML stored on behalf of that user.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
No action on the part of the XMPP Registrar  is necessary as a result of this document, since 'jabber:iq:private' is already a registered namespace.
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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.
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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".
3. 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/>.
4. 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/