OPML Files as Aggregators

Scripting News: 7/22/2004: "Note to aggregator developers: I'm doing a special aggregator for these feeds. But the list is open and will be maintained, so you can use it. It's a subtly different kind of subscription list, because it will change, you should subscribe to the OPML not to the feeds contained in the OPML. It's a chance to do a little upgrade among the aggregators for the DNC. I did it this way on purpose. It's the "neat net tricks" part of the barn-raising. There should always be a developer angle, imho."

Dave, this is a fascinating idea. I work for an aggregator but I'm not sure exactly how to implement this. When I go to that link I get an OPML file; how would I modify my aggregator to be able to get updates from an OPML file? I love that idea of OPML files being able to represent an aggregator for a specific subject. Can you flesh this out some more?