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With Internet Explorer 8 at an advanced stage of development, Microsoft's IE team is determined to avoid the compatibility problems that caused version 7 to incorrectly render pages that had been coded according to web standards.

This was not because IE7 did not support web standards, far from it, explains Chris Wilson IE Platform Architect.

The problem was that the developers of standards-compliant sites had added code to work around the "shortcomings or outright errors in IE6" because that is how they expected IE7 to behave.

"Web developers expected us, for example, to maintain our model for how content overflows its box, even in 'standards mode', even though it didn't follow the specification - because they'd already made their content work with our model," he explains. "In many cases, these sites would have worked better if they had served IE7 the same content and stylesheets they were serving when visited with a non-IE browser, but they had 'fixed their content' for IE. Sites didn't work, and users experienced problems."

The IE team at Microsoft, together with The Web Standards Project (WASP), realised that the problem lay in the way that web pages identify themselves to a browser. Typically a page will have a DOCTYPE element which identifies which version of HTML it has been coded in. This is fine, assuming it complies to that version of the standard. If it doesn't then the browser is left to guess.

Quirks mode

Currently all browser have one more "quirks" modes that deals with this problem and a standards mode. Microsoft is proposing a third

"We believe this approach has the best blend of allowing web developers to easily write code to interoperable web standards while not causing compatibility problems with current content," Wilson said "We also think this approach allows developers to opt in to standards behaviour on their own schedule and as it makes sense to them, instead of forcing developers into a responsive mode when a new version of IE has different behaviour on their current pages."

The idea is expanded in an article on A List Apart by WASP-Microsoft taskforce member Aaron Gustafsson, and the source of a nascent debate on W3C's Q&A blog.

Safari

Maciej Stachowiak, from the WebKit Safari development team, says that the issues that IE faces do not apply to browsers that have always strived to be standards compliant and do not share IE's "tough position" as the most widely used browser (the same applies to other minority browsers such as Firefox).

"The fixes we do for standards compliance rarely cause widespread destruction, and when they do, it's often a sign that the standards themselves may need revision," he wrote on the Surfin' Safari blog. "We do not get complaints from web content authors about their sites breaking, on the contrary we get a lot of praise for each version of the engine handling web sites better."

Consequently, the WebKit team has no intention of implementing version targeting in Safari.

"We think maintaining multiple versions of the engine would have many downsides for us and little upside," he said.