From Sam Ruby's blog:
The SEC started using RSS feeds two or three years ago to push information about XBRL filings received under the SEC's Voluntary Filing Program. See http://www.sec.gov/Archives/edgar/xbrlrss.xml
See the prior entry on this blog for a link to the iBlanket widget which makes use of one of the ATOM feeds.
You can go look at the Edgar system and see the ATOM feed here. Look for the little orange icon, click on it. You can read the feed in your browser, but the important thing to understand is that a computer application can read this also.
Basically, according to a IRWebReport blog entry, each filer to the SEC has its own ATOM feed which a user can subscribe to. Imagine that the ATOM feed making you aware of information in an XBRL filing. A computer application watches the ATOM feed, becomes aware of a new filing, reads the information from the XBRL filing, and updates your internal analysis models or other applications. That is extremely powerful.