Internet Explorer 10 brings support for many new useful features. However, there are still a large number of sites that do not use doctype. Therefore, browsers interpret them in quirks mode. However, because it is an old IE5 kernel, it is not possible to use the new HTML5 techniques. Therefore, IE10 replaces the old quirks mode with a new one, which is supplemented with new techniques.
Recent versions of Internet Explorer have always brought a new rendering mode. Except for the seventh version, which showed that fundamental changes in the established regimes are not possible. The new mode usually adapts to recent standards and includes new features. As a rule, the old mode is not changed to maintain compatibility with older sites. Internet Explorer 10 is the exception and the rule at the same time. It features a fresh rendering mode with more thorough support for CSS3 and HTML5. It also brings a new rendering mode that will default to pages that don't have a doctype. This is an old adaptive mode with new features like <canvas>, <audio>, and <video>.
If your pages are made with the intention of throwing the browser mode into quirks mode, install Internet Explorer 10 Platform Preview 4 and check if they still render the same in the new quirks mode. If there is a problem, you can easily switch the browser mode back to IE5 times by adding:
<meta http-equiv="X-UA-Compatible" content="IE=5">You can also report deficiencies in the new quirks mode directly to the Internet Explorer developers on Microsoft Connect.
The article was written for the Czech MSDN Blog.