[whatwg] <meta http-equiv="X-UA-Compatible" content="IE=edge" />

Mikko Rantalainen mikko.rantalainen at peda.net
Wed Jan 23 03:45:25 PST 2008

Brenton Strine wrote:
> [IE8] won't render pages with
> the new standards-compatibility unless you explicitly
> tell it to with this meta tag:
> <meta http-equiv="X-UA-Compatible" content="IE=edge" />

> My thought is this (and I'm hoping other people will come
> up with better ideas). Give HTML the ability to declare
> specific technologies that it uses, such that if a
> browser supports that technology, it makes use of it.
> Sort of like using object detection in javascript instead
> of messing with the user agent string. For example,
> assume an amazing new image format comes out called
> AwesomeImg--Opera 11 supports it, but you're not sure
> when IE will. Maybe IE10. But you don't want to lock your
> site into IE10 mode because it might break in IE10, or
> IE10 might still not support all your features but IE11
> would have.

A feature like that would target a different problem: the problem that
author knows which features are available in different standards but
user agents do not yet support those features. The problem with this
method is that UAs may support "CSS 2.1" and advertise it but there are
bugs. Some content that has been designed for CSS 2.1 would not display
correctly if the UA supports CSS 2.1 but has some - perhaps minor - bug
in the implementation.

The X-UA-Compatible fights with the problem that content authors have no
clue about standards and think that if their content looks correct to
them when they try user agent X, then it's fine. The X-UA-Compatible is
designed so that the content author lists the UAs that he has confirmed
to display the content correctly.

I think the idea is pretty good but the IE8's implementation is
terrible. Instead of the currently proposed "solution" the author should
add X-UA-Compatible: IE=7 to their HTTP headers if they have checked
with IE7. IE8 should use its best standards mode by default and
downgrade to IE7 rendering if and only if the page says that it has been
tested only with IE7. The DOCTYPE switch should be used to switch to
real quirks mode for obviously non-standard content. As it has been
currently designed, the feature must be used to get the best (nearest to
the standard) rendering possible instead of requesting a special set of
quirks which is really needed for old and somewhat incorrectly authored

X-UA-Compatible: IE=X should be considered to mean "I don't know what
I'm doing but nevertheless the content looks the way I meant if you use
Internet Explorer version X".


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