This Pace specifies the addition of a "related" link type for referring to external objects. It also proposes the addition of an optional advisory length attribute to the link element.
Related and Conflicting Proposals
The author of an entry may wish to include references to external objects related to the entry, for example, video files, related web pages, related Atom feed entries, etc. Although such objects could be linked to using (X)HTML anchor tags in the content element, there may be cases where this is not workable (for example, if the atom:content is an image rather than text). It also may simply not be desirable (for example, if the author wishes to attach a list of links to source documents without actually including a list of anchor tags in the content).
While a content size specified within a feed can hardly be considered authoritative (since the external object could be modified independently of the feed entry, not to mention the fact that the size could be reported incorrectly in the first place), it might still be useful advisory information to obviate the need to HEAD the resource to get an idea of its size.
The proposed changes would provide a basis for users of Atom clients to decide whether to prefetch the related content (the client could provide preferences to control whether content would be prefetched based on MIME type and/or size).
Add the following to section 5.4.1 of the Atom API Specification
The URI in the href attribute points to content related to the containing resource.
Also, add section 5.4.5 as follows:
The "length" attribute indicates an advisory length of the linked content in octets; it MAY be used as a hint to determine the content length of the representation returned when the URI in the href attribute is dereferenced. Note that the length attribute does not override the actual content length of the representation as reported by the underlying protocol.
<link rel="related" type="video/quicktime" title="Dad wipes out on the slopes!" length="3000000" href="http://www.xyz.com/~gecko/skiing.mov" />
<link rel="related" type="text/html" title="Environmental Impact Statement" href="http://www.xyz.com/airport/proposals/newrunway/eis.html" />
This proposal does not add any requirements for feed publishers. If they wish to enable publishing related links, they would need to provide a UI for doing so. It requires clients to support some method of exposing a new type of link in their UIs.
[AntoneRoundy] Might "content-length" be better than "size". Either is good by me.
See Also: PaceLinkDelicious