Linking Resources without HTML, XHTML, Atom...

In HTML you can link to alternative versions of your HTML using the link tag:
<link rel="alternate" type="application/rss+xml" title="RSS Feed"
href="report.rss" />

There is a way to do linking just using HTTP through the LINK header (as seen in POWDER. It looks very similar but is more powerful, from the IETF draf document:

Link: <http://example.org/>; rel="index start";
rel="http://example.net/relation/other" rev=copyright


Defines 4 links for http://example.org/, three outbound (index, start and http://example.net/relation/other) and one inbound (copyright).

More information: HTTP Status Report and LinkHeader.