Atom, the well-formed format

The issue of quality has been on the mailing list a lot recently, along with many blog posts referring to Postel's Law. Although there are doubters, the consensus seems to be that insisting on feed producers sticking to the spec, in particular XML well-formedness, is the way forward. The idea being that developer's time is better spent on creating cool features than disentangling tag soup.
Tim Bray described how this might work in the market :

An Atom feed is going to be defined as an XML document, which means that if it’s not well-formed then it’s not Atom. All it needs is for one (I repeat, one) popular newsreader with a large installed base to enforce this policy (stop parsing and display an error to the subscriber) to turn this from de jure to de facto reality. This works because Atom doesn’t have an installed base. Let’s name names; if any one of NetNewsWire or FeedDemon or Radio adopted this policy for Atom, it would be game over; people who’ve gotten used to these aggregators are not going to switch clients because some upstream feed producer is a bozo.

Within hours of this post the developers of both NetNewsWire and FeedDemon announced they will both have the policy ill-formed XML being considered an error.

Meanwhile, Sam Ruby is being scientific about valid RSS, with a sample feed for everyone to try in their validator.