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Archive for November, 2007 Web service API

Tuesday, November 27th, 2007 has had a Web service API for a while. It has not had documentation, though. This has now changed: Web service API docs.

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Validating attribute values

Monday, November 26th, 2007

Traditionally, SGML-based HTML validation has treated most attribute values as “anything goes” strings. This has meant that all kinds of bogus values have passed as valid. W3C XML Schema added a fixed set of datatypes. The spec is mostly useless for HTML5 validation, since the HTML5 microsyntaxes do not match exactly the XSD datatypes for the same concepts. XSD regular expressions were suitable for representing the syntax of a number of HTML5 microsyntaxes, though. XSD datatypes can be used from RELAX NG and used to XSD regular expressions for many HTML5 microsyntaxes.

The problem with using XSD regular expressions has been that they are not user-friendly. When an attribute value did not match the required regular expression, the UI told the user that the attribute value was “bad”. Nothing else.

Fortunately, unlike XSD, RELAX NG allows pluggable datatype libraries. A datatype library is a library written in a general-purpose programming language. The RELAX NG engine calls the library to check if a string conforms to a named datatype. has used this approach for a long time for the more complex microsyntaxes in HTML5.

I have recently made an effort to move away from XSD regular expressions to a more comprehensive custom datatype library. Even though as a formalism regular expressions are sufficient for many syntaxes, writing checking by hand allows more useful error messages in cases of failure. Moreover, having identifiers for the datatypes makes it possible to tell which datatype failed as opposed to the UI being able to tell that some regular expression failed under the hood. This allows the UI to pull in per-datatype advice from a wiki page.

In addition to improving the user experience with previously supported microsyntaxes such as integers, I have implemented support for previously unsupported microsyntaxes such as MIME types and Media Queries.

There is still work to do. For example, the syntaxes for accept-charset and WF2 type=email are not done. data: and mailto: IRIs are not properly validated yet. The syntaxes for image map coordinates still use XSD regular expressions. The advice on the wiki page is far from complete. (You can help!)

For the parts already implemented, please try the new features out and let me know what needs improvement.

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Wiki collaboration to describe HTML5 microsyntaxes

Tuesday, November 20th, 2007

Currently, mines the HTML 5 spec for UI text describing permissible content models, element contexts and element-specific attributes. The text is shown when an element or attribute is misplaced on missing.

Unfortunately, the spec does not contain similarly extractable text for microsyntax descriptions. Microsyntaxes are syntaxes that appear mostly in attribute values—for example, HTML5 integer, Web Forms 2.0 week, RFC 2616 media types (aka. MIME types) or CSS3 Media Queries.

Based on IRC discussions, there is interest in producing the descriptions collaboratively. To that end, I have seeded the WHATWG wiki with a page for microsyntax descriptions. If you would like to help make validator messages better, please feel free to edit the wiki (under the MIT license).

Posted in Conformance Checking, Syntax | 1 Comment »

The WHATWG at the W3C technical plenary

Wednesday, November 7th, 2007

The W3C is having its technical plenary day today, and a number of WHATWG contributors are there. It's hard to participate remotely in this event, but you can watch and listen — the W3C is publishing an audio stream (in Ogg; a Java applet alternative is available too), and has commissioned realtime captioning for the event. There's also W3C IRC channel on the topic on, port 6665, channel #tp, password beantown * (a single asterisk) (it's not clear why there's a password, just go with it) (no password anymore). You can also chat with WHATWG contributors who are present at the event on our own IRC channel.

The agenda for the day is available from the W3C site. Don't forget to adjust the times from the Boston timezone to your timezone if you want to listen to a particular session.

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