hint for best practices related to usage of the X-UA-Compatible meta tag and response header
npm install @hint/hint-highest-available-document-modehighest-available-document-mode)highest-available-document-mode warns against not informing browsers
that support document modes to use the highest one available.
Internet Explorer 8/9/10 support [document compatibility modes][doc
modes]. Because of this, even if the site’s visitor is using, let’s
say, Internet Explorer 9, it’s possible that Internet Explorer will
not use the latest rendering engine, and instead, decide to render
your page using the Internet Explorer 5.5 rendering engine.
Serving the page with the following HTTP response header:
``text`
X-UA-Compatible: ie=edge
or specifying the x-ua-compatible meta tag:
`html`
will force Internet Explorer 8/9/10 to render the page in the highest
available mode in [the various cases when it may not][ie complications],
and therefore, ensure that anyone browsing the site from those browsers
will get the best possible user experience that browser can offer.
Of the two methods, sending the HTTP response header instead of using
the meta tag is recommended, as the latter will not always workDisplay intranet sites in Compatibility
(e.g.: if the site is served on a non-standard port, as Internet
Explorer’s preference option
View is checked by default).
Notes:
* If the meta is used, it should to be included in the
before all other tags except for the and the other
tags.* Appending
chrome=1 to the value of the HTTP response header or
the meta tag is not recommended as [Chrome Frame has been
deprecated][chrome frame] for quite some time.What does the hint check?
By default, the hint checks if the
X-UA-Compatible response header
is sent with the value of IE=edge, and that the meta tag isn’t
used.$3
X-UA-Compatible response header is not sent:`text
HTTP/... 200 OK...
`X-UA-Compatible response header is sent with a value different
than ie=edge:`text
HTTP/... 200 OK...
X-UA-Compatible: IE=7
``text
HTTP/... 200 OK...
X-UA-Compatible: ie=edge,chrome=1
`X-UA-Compatible response header is sent, but the meta tag is
also specified:`text
HTTP/... 200 OK...
X-UA-Compatible: ie=edge
``html
example
...
...
`$3
`text
HTTP/... 200 OK...
X-UA-Compatible: ie=edge
`The hint can be configured to require
the
X-UA-Compatible meta tag. This option is indicated mainly for
the case when the HTTP response header cannot be set.$3
X-UA-Compatible meta tag is not specified:`html
example
...
...
`X-UA-Compatible meta tag is specified with a value different than
ie=edge:`html
example
...
...
``html
example
...
...
`X-UA-Compatible meta tag is specified in the :`html
example
...
...
...
`X-UA-Compatible meta tag is specified in the , but it’s
not included before all other tags except for the and the
other tags:`html
example
...
...
`$3
`text
HTTP/... 200 OK...
X-UA-Compatible: ie=edge
``html
example
...
...
`How to configure the server to pass this hint
How to configure Apache
Apache can be configured to add or remove the
X-UA-Compatible
header using the [Header directive][header directive].$3
`apache
# Because
mod_headers cannot match based on the content-type,
# and the X-UA-Compatible response header should only be sent
# for HTML documents and not for the other resources, the following
# workaround needs to be done. # 1) Add the header to all resources.
Header set X-UA-Compatible "IE=edge"
# 2) Remove the header for all resources that should not have it.
Header unset X-UA-Compatible
`Removing the
X-UA-Compatible header on ApacheIf the header is sent, in most cases, to make Apache stop sending
the
X-UA-Compatible requires removing the configuration that adds
it (i.e.: something such as Header set X-UA-Compatible "IE=edge").
However, if the header is added from somewhere in the stack (e.g.
the framework level, language level such as PHP, etc.), and that
cannot be changed, you can try to remove it at the Apache level,
using the following:`apache
Header unset X-UA-Compatible
`Note that:
* The above snippets work with Apache
v2.2.0+, but you need to have
[mod_headers][mod_headers] [enabled][how to enable apache modules]
in order for them to take effect.* If you have access to the [main Apache configuration file][main
apache conf file] (usually called
httpd.conf), you should add
the logic in, for example, a [][apache directory]
section in that file. This is usually the recommended way as
[using .htaccess files slows down][htaccess is slow] Apache! If you don't have access to the main configuration file (quite
common with hosting services), add the snippets in a
.htaccess
file in the root of the web site/app.For the complete set of configurations, not just for this rule, see
the [Apache server configuration related documentation][apache config].
How to configure IIS
$3
To add the
X-UA-Compatible header you can use a [URL rewrite
rule][url rewrite] rule that matches the text/html content-type
header of a response and adds it:`xml
`Note that if your site uses a mime type different than
text/html
(e.g.: application/xhtml+xml) to serve HTML content, you'll have
to update the value of pattern.Removing the
X-UA-Compatible header on IISIf the header is set by IIS using the above technique, removing the
code should be enough to stop sending it.
If the header is set at the application level you can use the following:
`xml
`Note that:
* The above snippet works with IIS 7+.
* You should use the above snippet in the
web.config of your
application.For the complete set of configurations, not just for this rule,
see the [IIS server configuration related documentation][iis config].
Can the hint be configured?
requireMetaElement can be set to true to allow and require the use of
meta tag.In the [
.hintrc][hintrc] file:`json
{
"connector": {...},
"formatters": [...],
"hints": {
"highest-available-document-mode": [ "warning", {
"requireMetaElement": true
}],
...
},
...
}
`Also, note that this hint takes into consideration the [targeted
browsers][targeted browsers], and if Internet Explorer 8/9/10 aren’t
among them, it will suggest removing the
meta tag and/or not sending
the HTTP response header.How to use this hint?
This package is installed automatically by webhint:
`bash
npm install hint --save-dev
`To use it, activate it via the [
.hintrc][hintrc] configuration file:`json
{
"connector": {...},
"formatters": [...],
"hints": {
"highest-available-document-mode": "error",
...
},
"parsers": [...],
...
}
`Note: The recommended way of running webhint is as a
devDependency` of* [Internet Explorer 8/9/10 Complications][ie complications]
* Specifying legacy document modes
[chrome frame]: https://blog.chromium.org/2013/06/retiring-chrome-frame.html
[doc modes]: https://msdn.microsoft.com/en-us/library/cc288325.aspx
[hintrc]: https://webhint.io/docs/user-guide/configuring-webhint/summary/
[ie complications]: https://hsivonen.fi/doctype/#ie8
[targeted browsers]: https://webhint.io/docs/user-guide/configuring-webhint/browser-context/
[apache config]: https://webhint.io/docs/user-guide/server-configurations/apache/
[apache directory]: https://httpd.apache.org/docs/current/mod/core.html#directory
[header directive]: https://httpd.apache.org/docs/current/mod/mod_headers.html#header
[how to enable apache modules]: https://github.com/h5bp/server-configs-apache/tree/7eb30da6a06ec4fc24daf33c75b7bd86f9ad1f68#enable-apache-httpd-modules
[htaccess is slow]: https://httpd.apache.org/docs/current/howto/htaccess.html#when
[main apache conf file]: https://httpd.apache.org/docs/current/configuring.html#main
[mod_headers]: https://httpd.apache.org/docs/current/mod/mod_headers.html
[mod_mime]: https://httpd.apache.org/docs/current/mod/mod_mime.html
[iis config]: https://webhint.io/docs/user-guide/server-configurations/iis/
[url rewrite]: https://docs.microsoft.com/en-us/iis/extensions/url-rewrite-module/using-the-url-rewrite-module