OPML 2.0 as a namespace

Wednesday, July 18, 2007 by Dave Winer.

First, I want to be able to use elements of OPML 2.0 in my RSS feeds. I'm already doing it on an experimental basis, in the RSS 2.0 feed for TwitterGrams. 

http://mp3.twittergram.com/rss.xml  

Note that it declares a "opml2" as a namespace at the head of the document, and it uses as the URI for the namespace, the OPML 2.0 spec. Apparently this breaks nothing, I've had no complaints about this feed. That doesn't mean there are no problems, however none have been reported. 

The question is, can we put a namespace declaration at the head of an OPML file without breaking processors. When we tried to do this when RSS 2.0 was in its final shakeout (almost five years ago), it broke a bunch of apps and we had to back out of the idea. 

It may be a problem with OPML as well. The point of this post is to ask for opinions of XML experts. Breakage of existing apps is not an option (see this post by Dare Obasanjo for an idea why). 

Don Park weighs in.