The <data/> element can be used in conjunction with &xep0071; and the cid: URL scheme to point to binary data that is provided in-band within a &MESSAGE; stanza.

Once the data is provided, a subsequent message in the same session can refer to the data again without including it.

If the receiving entity has not cached the data, it can request the data as described in the next section.

Data can be requested and transferred using the XMPP &IQ; stanza type by making reference to the 'cid' of the data to be retrieved. In particular, the requesting entity can request data by sending an IQ-get containing an empty <data/> element with a 'cid' attribute.

The responding entity then would either return an error (e.g., ¬found; if it does not have data matching the Content-ID) or return the data.

This specification does not place limits on the entities from which data can be requested. In particular, such an entity need not be the "owner" of the data (e.g., it could be a peer in a chatroom or whiteboarding session).

In addition, bits of data could be hosted by XMPP servers, distributed via &xep0060; nodes, or included in data collections that are available via HTTP (e.g., emoticon sets). Such data could be identified by the value of the 'cid' attribute, but methods for specifying those values are out of scope for this specification.

&xep0221; describes how to include a media element in &xep0004;, e.g. for the purpose of placing a human-viewable "CAPTCHA" in a form that is used for &xep0158; or &xep0077;. The <media/> element described in XEP-0221 contains one or more <uri/> elements (which point to locations where the media can be downloaded, e.g. via HTTP) as well as a <data/> element that includes the data itself. The proposed <media/> element could be redefined to contain a <data/> element as described herein and shown in the following example.

The media could then be included in a data form.

A previous proposal See <http://www.xmpp.org/extensions/inbox/file-preview.html>. described a method for including a thumbnail or file preview in a file transfer request. Such a preview can be included using the <data/> element, as shown below. However, a preview SHOULD not be included unless the receiving entity advertises (via &xep0030; or &xep0115;) support for the "urn:xmpp:tmp:file-preview" service discovery feature &NSNOTE;.

Until this specification advances to a status of Draft, its associated namespace shall be "urn:xmpp:tmp:data-element"; upon advancement of this specification, the ®ISTRAR; shall issue a permanent namespace in accordance with the process defined in Section 4 of &xep0053;.

If an entity is willing to accept data elements in file transfer requests for the purpose of previewing the file to be sent, it SHOULD advertise support for the "urn:xmpp:tmp:file-preview" feature.

The registry submission is as follows.