Interoperable HTML5 Quirks Mode in IE10

December 14th, 2011

fourth IE10 platform preview
includes enhanced HTML5 support by using an interoperable quirks mode based on the behavior defined in HTML5.
This HTML5-based quirks mode is the default quirks mode in IE10.

Users and Web developers want sites to just work across browsers.
A key part of this is making HTML, CSS, and JavaScript work in the same way across implementations.
HTML5 facilitates cross-browser consistency by defining parts of the Web platform previously left unspecified.
This largely involves the
HTML5 parsing rules,
but also includes parts about
in quirks mode.

IE10’s HTML5 quirks mode is used for pages without a DOCTYPE or with a legacy DOCTYPE
as defined in HTML5.
Like HTML5 and other browsers, the behavior of IE10’s quirks mode is the same as standards mode with select quirks applied.
This means features like <canvas>, <audio>, and <video> remain available.
Most importantly this aligns IE10’s quirks mode with the behavior of other browsers,
so pages missing a DOCTYPE run consistently across implementations.

Developers can quickly identify which mode a page uses via the F12 developer tools.
The latest HTML5 standards and quirks modes are now listed as Standards and Quirks.
Legacy modes are still listed by the version of IE that introduced them.
IE’s legacy quirks mode is now referred to as Internet Explorer 5 quirks.

IE10 continues to use Internet Explorer 5 quirks in Compatibility View for pages without a DOCTYPE,
and for pages that opt-in via X-UA-Compatible.

<meta http-equiv="X-UA-Compatible" content="IE=5">

Call to Action

HTML5 defines quirks mode for compatibility and interoperability,
but you should continue to author new sites for standards mode by using <!DOCTYPE html> at the top of your pages.
Please help ensure IE10’s HTML5 quirks mode works correctly by reporting issues via

—Tony Ross, Program Manager, Internet Explorer