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relEnclosure is a simple, open, format for indicating files to cache which is embeddable in (X)HTML, Atom, RSS, and arbitrary XML. relEnclosure is an elemental microformat, one of several microformat open standards.

Draft Specification 2005-06-21


Kevin Marks, Technorati, Inc.


This specification is (C) 2004-2022 by the authors. However, the authors intend to submit (or already have submitted, see details in the spec) this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C. Anyone wishing to contribute should read their copyright principles, policies and licenses (e.g. the GMPG Principles) and agree to them, including licensing of all contributions under all required licenses (e.g. CC-by 1.0 and later), before contributing.


This specification is subject to a royalty free patent policy, e.g. per the W3C Patent Policy, and IETF RFC3667 & RFC3668.


relEnclosure is one of several microformats. By adding rel="enclosure" to a hyperlink, a page indicates that the destination of that hyperlink is intended to be downloaded and cached. E.g. with the following hyperlink:

<a href="" rel="enclosure">WWDC 2005 Keynote with chapters</a>

the author indicates that the movie should be downloaded.

Multiple Enclosures

Multiple such rel="enclosure" hyperlinks indicate that several media items should be downloaded.

Question: What if there are several alternative formats, such as high- and low-bandwidth recordings? rel="alternate" is already defined in XHTML for this purpose, so how should it interact with this new rel tag?

XMDP profile

<dl class="profile">
 <dt id="rel">rel</dt>
   <a rel="help" href="">
     HTML4 definition of the 'rel' attribute.</a>  
   Here is an additional value.</p>
   <dt id="enclosure"> enclosure </dt>
   <dd>Indicates that the referred resource is intended to be downloaded and cached</dd>

normative references

informative references  The "rel" Attribute
  4.  The value "enclosure" signifies that the IRI in the value of the
      href attribute identifies a related resource which is potentially
      large in size and might require special handling.  For atom:link
      elements with rel="enclosure", the length attribute SHOULD be