Subscription lists defined in OPML 2.0 spec
The addition of subscription lists as a part of the OPML 2.0 spec is actually pretty significant, and I only just now felt it sink in. This has been one of the main uses of OPML up to now, and it's mostly been passed around by oral tradition and whatever news aggregator happened to do with it. Now there's documentation. If nothing else, that alone makes the OPML 2.0 spec worth the price of admission. From here on out, future use cases for OPML should follow the same lead, defining the semantics of their new node types and associated attributes.