Feeds and well-formed XML
Here in Windows, we're working hard on Windows Vista Beta 2, and we've recently been doing some work on how we parse feeds. — Our years of experience in with HTML in Internet Explorer have taught us the long-term pain that results from being too liberal with what you accept from others.
Context & Ripple Effects
This post lands mid-way through a week of RSS quality complaints from inside and around Microsoft. Days earlier, a Microsoft geek blogger had called out Wordpress.com's broken feeds and argued that RSS usability suffers when producers emit invalid markup, while Read/Write Web covered Microsoft's broader Web 2.0 push.
The significance: the Windows RSS Platform in Vista Beta 2 will become one of the highest-volume feed parsers on the planet, so its strictness decisions effectively become de facto standards for every publisher whose feed Windows users subscribe to.
First-order effects
- Publishers with malformed feeds — like the Wordpress.com cases already flagged by Microsoft bloggers — risk their content failing or degrading in Vista's built-in feed reader unless they fix validity now.
- The IE team institutionalizes a Postel-skeptic stance: instead of silently repairing bad input as browsers did with HTML, the Vista parser demands well-formed XML, shifting the correction burden upstream to feed generators.
Second-order effects
- Blogging tools and CMS vendors face pressure to validate output by default, since their customers' feeds are judged against a strict parser most of them don't control.
- Competing feed readers and aggregators must decide whether to match Windows' strictness for consistency or stay liberal, splitting the ecosystem into two compatibility tiers.
Third-order effects
- If the strict approach holds, feed validation becomes table stakes for publishing infrastructure — the same trajectory HTML tooling followed after browser quirks-mode pain — and aggregator market share becomes a lever for enforcing markup standards.
- The episode prefigures a recurring platform pattern: whoever ships the dominant consumer of a format quietly sets its effective spec, making parser policy an exercise of standard-setting power rather than a technical detail.
The trend: As syndicated formats move from hobbyist niches into mass-market operating systems, the dominant client's parsing strictness becomes the de facto enforcement mechanism for data-quality standards across the web.