"We accomplished with DOM Level 3 the original vision we had for the DOM application programming interface back in 1997," said Philippe le Hegaret, the W3C's DOM activity lead. "There are nearly seven years of experience in XML in it."
The DOM is the W3C's browser-neutral application programming interface (API) that lets Web authors use scripts to automatically update parts of a Web page with fresh information. The DOM can be used in applications from digital clocks to Web services. XML, or extensible markup language, is a W3C recommendation for creating task- or industry-specific markup languages that are more machine-readable than traditional Web pages or text documents.
Improvements to the DOM in Level 3 include a technique called bootstrapping that lets scripts designate what kind of DOM implementation the author wants to request. The DOM provides different implementations for different kinds of Web content, for example one for basic HTML pages and another for Scalable Vector Graphics (SVG) animations.
In another change, the DOM now supports name spaces in the W3C recommendations XPath and Web Services Description Language (WSDL). XML name spaces, which DOM Level 2 already supported, let browsers distinguish between tags that have the same names but belong to distinct XML dialects and have distinct functions.
XPath and WSDL name spaces moved beyond tags to govern some content as well, and DOM Level 3 now supports that extended functionality.
One analyst applauded the DOM revision, calling it part of a trend of maturing Web protocols that would lessen reliance on Microsoft's dominant Internet Explorer browser.
"The refined quality of the definition and the maturity we see in the other components suggests to us that this stuff is finally getting baked," said Jonathan Eunice, principal analyst with Illuminata. "It's not just in the DOM, it's in the XML parsers, and in the different programming languages like Perl and Java. And it all helps move the Web from being IE-only to letting you take your pick of browser."
Even as the W3C updated the DOM, it reiterated prior calls for Web developers to use it sparingly. That's because pages that rely on scripts are harder to automatically transform for people with disabilities.
"Avoiding scripting means better accessibility of the pages in general," le Hegaret said. HTML usually allows a browser user to perform an action with either mouse or keyboard. But scripts often provide only one option, which may render a page more difficult for people with disabilities to use. "Script developers don't always see the issues related to accessibility, and therefore don't handle them when they write their scripts."