Interoperable HTML5 Quirks Mode in IE10

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.

Screen shot of F12 Developer Tools’ Document Mode menu
F12 Developer Tools’ Document Mode menu

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

Comments (39)

  1. Randall says:

    Compatible backwards compatibility–nonstandard behaviors only when someone asked for them! Awesome–great step forward for the Web.

  2. Chris Poteet says:

    I hope, at some point, that the vision is to move away from X-UA-Compatible and all this different browser standards modes.

  3. Roel Monnens says:

    IE10 only needs an IE10 mode!!!!

    Please stop annoying us with these modes!

  4. Klimax says:

    @Chris Poteet 14 Dec 2011 11:23 AM:

    No sooner then fifty years…

  5. CnEY says:

    I was afraid of this.  Rather than updating quirks mode to be less quirky, you are adding a SECOND QUIRKS MODE.  Really?!  I'm dying here, guys!

    Perhaps I am experiencing the fatigue inherent in already having to support 5 IE versions even without 10, but please explain to me how adding TWO new vectors instead of one to web developers' test processes in IE10 helps *anybody*.

    And yes, when will we finally begin to jettison this cruft that is over 10 years old?  I realize IE has a broad customer base, but for crying out loud, the amount of backcompat cruft that's sticking around just for the sake of big heavy corporations that are too inept to update once every couple of decades is really wearing thin.

  6. Kirk says:

    For the love of God! Microsoft stop doing this "compatibility" stuff, you only need to support the latest web standards, this way you force people to migrate to the latest versions of their browsers, and web sites to develop using only standards; by doing this the only thing you are doing is supporting fragmentation of the web. Not liking this idea at all.

  7. Anon says:

    Is there some reason that the Internet Explorer 5 mode's shortcut is Alt+U instead of something like Alt+5? Alt+5 is unused as far as I know.

  8. Mark says:


    If you're writing HTML that triggers compatibility modes, it's your own fault. If you just use <!DOCTYPE html> and write standards-compliant code then you won't have to deal with the backwards compatibility modes.


    Cause they will suddenly fall in love with IE10 and modern standards instead of just not upgrading and sticking to OSes that cause Microsoft support headaches, right?

  9. Arieta says:

    Guys, read the post… it's written very confusingly!

    The new, updated quirks mode is used on any page that doesn't have a doctype. It works the same (supposedly) as the doctype-less quirks mode in Firefox, which indeed also changes things around when a doctype is not present. The OLD quirks mode is strictly used in COMPATIBILITY VIEW only. It's basically on life support, and will disappear, once sites are updated with proper standards compliant code. So this old mode may disappear sooner than you think.

    So basically IE10 will have the standard/quirks mode that all other browsers do, it just includes 4 "emulation" modes for lazy web devs who wrote browser-dependent code. This is a good compromise.

    However, we've still seen no confirmation on what new things the "IE10 quirks" support. Is it just "IE5 Quirks" with <canvas>, <audio>, and <video>, or will it include other new features like CSS3 as well?

    Also, I find the nomenclature "Quirks mode" and "IE5 Quirks" to be extremely confusing, as you can see from the replies in this blog. That should be remedied some way. Call it "IE5/7/8/9 Emulation" with the IE5 mode being "IE5 Emulation (old quirks mode)" or so. That's somewhat clearer. Make it apparent that those modes are for legacy compatibility and absolutely nothing else.

  10. Tony Ross [MSFT] says:


    Sorry if you found the post/nomenclature confusing, though your summary is correct. To your question on supported features: IE10's quirks mode supports the exact same set of features as IE10's standards mode. Other browsers have a similar relationship between their quirks and standards mode. I was just using <canvas>, <audio>, and <video> as examples.

  11. CnEY says:

    @Mark:  I realized some time after I commented that perhaps the perspective I happen to be coming from wasn't at all clear, and I apologize for that.

    The thing is, I happen to deal with (and contribute to) an open-source JavaScript library quite regularly, and this library (like others) aims to support both quirks and standards modes.  The fact that there are now two separate quirks modes to detect and deal with differently in IE10 is thus a huge stumbling block that these libraries will have to contend with.

    @Arieta: I can't speak for others, but at least on my part I'm specifically concerned with the addition of a 2nd quirks mode.  The presence of IE7-9 and IE5 quirks modes is not really unexpected; that kind of support has existed since IE8.

  12. Arieta says:

    @Tony Ross: Thanks for the confirmation. So it's the same as Standards mode, just with the most widespread positioning bugs tucked in, I gather. That's excellent – well, it's another step where IE is now up to par with the competition.

    Now if you guys only added good userscripts and userstyles support out of the box… The updated quirks mode will make a TON of firefox or chrome specific userscripts work from the getgo, but sadly there are only two decent userscripts plugin for IE, and they are both unupdated and buggy (TrixIE and IEpro). There isn't any initiative to write IE plugins sadly, so it would be really, really cool if you guys made this a built-in feature.

  13. The question I have is, Why does anyone use Quirks mode? Is adding <!DOCTYPE html> at the top of Web pages too much work? Is there some benefit to using Quirks modes instead of Standards mode?

    I don't get it. Why deal with Quirks mode at all? Just add a DOCTYPE and be done.

  14. ErikF says:

    @CnEY, AFAICT, the only pages that should be using the IE5 compatibility mode are old pages that aren't going to be upgraded. As that is the case, don't bother coding anything for that case because it's these solely to support obsolete, read-only stuff!

    @IE: Are there any plans in place to allow for shims like what is done with Win32 programs? This seems like it makes a lot more sense from the perspective of feature testing as opposed to version checking, and it would allow developers to progressively turn off compatibility stuff as they upgrade old sites.

  15. Arieta says:

    @Ted Johnson: Imagine this simple scenario. Someone has a webpage that functions correctly in quirks mode, on all different browsers including IE. Switching to standards mode (on any browser or compatibility mode) completely breaks the functioning design. Now, this person has a few choices:

    – redesign the page

    – fix the current design to work in standards mode

    – leave it as-is, since it works in quirks mode anyway. If it's not broken…

    Now, this person may not have the talent/time/funds to alter the code. Or this person just doesn't want the site to chance it's looks in any way, either because of community backslash or because the current code does everything that is needed.

    And that's how we end up with sites like 4chan using old, outdated code in quirks mode yet still serving millions of users daily. You can actually make the site look and fucntion as a modern "web 2.0" site, with userscripts and userstyles… none which are properly possible with Internet Explorer right now. That's why I'm glad that Quirks mode is updated. Though, with my luck, compatibility with IEPro (a plugin that can support userscripts) will be utterly destroyed with IE10, so I won't win much.

  16. @Arieta: Yes, I fully understand the value of not breaking existing pages. That is precisely why IE has legacy document modes. What I don't understand is why new work, including work intended to showcase new HTML5 features, is done in Quirks mode.

  17. Arieta says:

    I suppose one principle could be so IE10 performs equal to the competition even under the hands of inept/uneducated coders. Both for new pages and old ones.

  18. Harry Richter says:


    As the connect site seems to be down and I need an answer quickly I’m posting this here in the hope that somebody can help me:

    Is there a size restriction for .jpg images that can be shown in IE9 and later?

    While trying to see an image with 41999 x 9171 px I only get the “broken”-icon (red square with white cross).


  19. user says:

    I wanted to thank you IE guys for such a good product and remind you that you need to work on it's memory management. sometimes I see almost 200mb memory usage by one of Iexplorer processes so I start closing tabs, after closing almost all tabs task manager shows that specific process still uses huge amount of memory… what? so I have to quit the browser entirly and reopen all the tabs I was working on, which means a lot of copy pastes

  20. Dave says:

    Currently under the Compatibility View Settings menu, the check box for 'Display intranet sites in Compatibility View' defaults to selected.  Are there any plans to make this default to unselected — perhaps in Internet Explorer 11?

    Keep up the good work!

  21. ieblog says:

    @Harry Richter: Your 41999 x 9171 pixel JPEG expands to about 1.5GB of data in the 32 bit-per-pixel format used for rendering images to the display. In 32-bit IE, this likely leads to an internal "out of memory" error. We think 64-bit IE should display the image.

  22. JM says:

    @ieblog 64-bit Internet Explorer could be the solution if only you'd make it usable. Please implement JIT compiler, full integration to Start menu and other features so that we'd be able to use full potential of 64-bit OS.

  23. Steve says:

    @Harry Richter – although I commend the effort to help find bugs.. please tell me that you don't actually try to load a 1.5GB image (or one that is 41,999 x 9,171) in your production environment!  I'm ok with the theory of no limits, but for usability this sounds waaaaaaay beyond reasonable expectations.

  24. Harry Richter says:

    @ ieblog

    Thanks for your answer, but no, IE9 64bit (9.0.8112.16421) does not display the image either. I get a different icon though: blue circle with diagonal line.

    @ Steve

    The question was: should I upload a picture to a forum that gives you the possibility to see the original image (a panoramic 360° view). I can of course reduce the size, but if it works, why should I not go with the original? The jpg is 46.7M! It is not an everyday application – I agree – but if it works, and makes sense for the readers of said forum – why not?


  25. Arieta says:

    @Harry Richter: The blue circle with diagonal line is the "adblocked" icon, however when the IE9 adblock is enabled, the normal red x globally changes to that even on 404 errors and such. Not sure if that's a bug or a feature.

  26. Harry Richter says:

    @ Arieta

    Thanks for reminding me, but the "adblock" aka tracking protection is not enabled on this computer. Also viewing local content is enabled and all is working properly, because I can see an image with 27108 x 5224 px just fine. Only the "really large" photos show this behaviour.


  27. In IE9, about:blank is displayed in quirks mode because of its lack of doctype declaration (<HTML></HTML>)

    This causes IE to display an ugly gray border around the page.

  28. ieblog says:

    @Harry Richter: Can you provide me URLs to your very large photos? You may email them to me using the Email Blog Author link in the top right box of this blog if you don't want to post them here.

  29. enlightenment says:

    Is HTML5 WebGL available in IE Quirks mode? Or will it only be available in IE HTML5 standards mode?

  30. Klimax says:


    There is no such thing as "HTML5 WebGL". What you eman is nonstandard stuff under name WebGL and due to various reasons it is not supported nor is it so far planned. No matter what mode you use. (Currently primary reason is security – kernel hosts graphics drivers – and absolute reliance on OpenGL, which is implemented by GPU vendors as Microsoft no longer ships their own)

  31. Randall says:

    @Ted Johnson: HTML5 features in Quirks mode could be useful when you're forced to post new content in an old wrapper — e.g., your new blog post can use a video tag even if it's in an old quirky blog template.

    But yeah, in a strong majority of cases you might as well just add a DOCTYPE.

  32. Arieta says:

    antiufo: How much time you spend looking at about:blank for this to be a problem?

  33. Arieta says:

    By the way, does anybody have a link to IE10 PP2? The link at IETestdrive points to the 4th, windows 8 only platform preview. I've had to reinstall recently and I didn't have the installer saved.

  34. Tal says:


    Important question:

    What is the difference between "interoperable quirks mode" and "ie5 quirks mode" ? (beside additional html5 support)

    Will old websites without doctype will work exactly the same in interoperable quirks mode as they worked before in IE7/IE8 legacy quirks mode? or it may fail in some cases?



  35. Artemus Folkmore says:

    "For the love of God! Microsoft stop doing this "compatibility" stuff, you only need to support the latest web standards, this way you force people to migrate to the latest versions of their browsers"

    For Christ's sake, have you ever heard about corporate environments that rely on web-based Intranet interfaces developed for IE6 and 7? Thank god at least Microsoft cares about businesses instead of caring just about the needs of the Children of Facebook.

  36. Anton says:

    quirks mode??? WTF?!!! enough of this garbage!!!!

  37. P Cause says:

    I would like someone from the IE team to explain how it is that a browser built by an MS team for Windows is less stable than one built by Google.  I have tried to stay with IE and evangelized the browser, but it is constantly crashing on my.  I have disabled all addons and it still happens.  1-3 times a day in normal browsing.  If I switch to Chrome it simply doesn't crash.  And, it is pretty difficult to build a simple IE addon while it is pretty trivial and relatively safe in Chrome as they allow one to write extensions in javascrpt.  Add to this the slow pace of updates of new functionality, the lack of regular betas for IT pros even those who pay for an MSDN subscription and one has to wonder whether or not it is worth it to stay with IE.

    I know IE10 is coming but we still see too few developer updates, I still can't create an extension in javascrip and I have little hope for better stability.

  38. 模式化 says:

    微软  是品牌的象征  但是在IE10的互操作HTML5的Quirks模式中  IE10只起到了高级 而不名牌的一个软件