Add to the predefined link@rel values "alternate" and "related" two other predefined values: "enclosure" and "image". Add a "length" attribute to Link constructs.
Instead of "enclosure", can we use "attachment"? While "enclosure" may be understood by RSS people, "attachment" has been used for a long time (e-mail) and has a clear meaning to anybody somewhat familiar with the Internet or computers.
Related and Conflicting Proposals
Feature parity with RSS 2.0
I. Add to 4.2.2:
atom:head elements MUST NOT contain more than one atom:link element with a rel attribute value of "image". atom:head elements MUST NOT contain an atom:link element with a rel attribute value of "enclosure".
II. Add to 5.2:
atom:entry elements MUST NOT contain an atom:link element with a rel attribute value of "image".
III. Modify PaceFieldingLinks as follows:
=== 3.5.2 Registry of Link Relations === This registry is maintained by IANA and initially contains the four values "alternate", "related", "enclosure", and "image". New assignments must be approved by the IESG. Requests should be made by mail to IANA, which will then forward the request to the IESG requesting approval. The request should contain discussion of at least the following four topics: * Common name for link type. * Description of link type semantics. * Expected display characteristics. * Security considerations. The value "alternate" signifies that the URI in the value of the href attribute identifies an alternate version of the resource described by the containing element. The value "related" signifies that the URI in the value of the href attribute identifies a resource to which the resource described by the containing atom:feed or atom:entry element is related. For example, the feed for a site which discusses the performance of the search engine at "http://search.example.com" might contain, as a child of atom:head: <link rel="related" href="http://search.example.com/"> An identical link might appear as a child of any atom:entry whose content contains a discussion of that same search engine. The value "enclosure" signifies that the URI in the value of the href attribute identifies a related resource which is potentially large in size and may require special handling by consuming software. For Link constructs with rel="enclosure", the length attribute SHOULD be provided. The value "image" signifies that the URI in the the value of the href attribute identifies an image which provides visual identification for a feed. The image SHOULD have an aspect ratio of 2 (horizontal) to 1 (vertical).
=== 3.5.4 "length" attribute === This attribute's value MUST be an integer number which gives the expected size in bytes of the representation received by dereferencing the URI in the value of the href attribute. Link constructs MAY have a length attribute.