Validome
There’s a new validator out there (at least new to me), that not only validates HTML, XHTML, WML, XML, DTD-Schema, and Google Sitemaps, but also is an “Advanced” Feed-Validator for RSS and Atom. It does appear to be pretty good, and as the development appears to be test-driven I'm confident that it will not only stay that way, but will continue to get better as more people use it.
I took a look at the 458 Atom 1.0 test cases defined (the Feed Validator currently has 763), and found a few items worthy of note, though some of these issues affected multiple tests.
| test | description | validation | comments | |
|---|---|---|---|---|
| 100 | extending link elements | FeedValidator | Validome | Places where I assert that Validome deviates from the specification. |
| 106 | rel attribute with relative IRI | FeedValidator | Validome | |
| 150 | entry document with no author | FeedValidator | Validome | |
| 185 | scheme-attribute with a relative IRI | FeedValidator | Validome | |
| 292 | content element with a src attribute | FeedValidator | Validome | Feeds where the FeedValidator reports on more than Validome does. |
| 335 | multiple category elements | FeedValidator | Validome |
I didn’t look as closely at the other feed formats, but did take a quick pass.
Validome does pay special attention to Mime types and charsets, issuing warnings when the Atom mime type isn't used for Atom feeds, and disallowing the unregistered but popular application/rss+xml.
While Validome says it will validate 0.91, the NetScape version of this specification required a DOCTYPE, and this validator does not support feeds with DTDs. It also seems to prefer the UserLand spelling of textInput.
Validome validates 0.92, which says that all sub-elements of item are optional. That spec also says that any 0.92 source is a valid 2.0 source, and yet the RSS 2.0 spec says that at least one of title or description must be present. At least one of these three statements must be false. The feed validator takes a more conservative route and requires at least one of title or description independent of the RSS version; Validome permits 0.92 feeds to omit both.
Validome doesn’t seem to verify that RSS 1.0 extensions are valid RDF/XML.
With reguard to RSS 2.0, I'd suggest that Validome take a look at the profile work being done by the RSS Advisory Board. I'd also be curious to see how it handles the prenially problematic RFC 822 style dates that the RSS 2.0 specification mandates.
Validome does validate Atom 0.3, which should make Matt happy.