https://stackoverflow.com/questions/6771258/what-does-meta-http-equiv-x-ua-compatible-content-ie-edge-do

What’s the difference if one web page starts with

<!DOCTYPE html&> 
<html&> 
  <head&> 
    <meta http-equiv="X-UA-Compatible" content="IE=edge"&>

and If page starts with

<!DOCTYPE html&> 
<html&> 
  <head&> 
     <!-- without X-UA-Compatible meta --&>

This answer was posted several years ago and now the question really should beshould you even consider using theX-UA-Compatibletag on your site?with the changes Microsoft has made to its browsers (more on those below).

Depending upon what Microsoft browsers you support you may not need to continue using theX-UA-Compatibletag. If you need to support IE 9 or IE 8, then I would recommend using the tag. If you only support the latest browsers (IE 11 and/or Edge) then I would consider dropping this tag altogether. If you use Twitter Bootstrap and need to eliminate validation warnings, this tag must appear in its specified order. Additional info below:

The X-UA-Compatible meta tag allows web authors to choose what version of Internet Explorer the page should be rendered as. IE11 has made changes to these modes; see the IE11 note below.Microsoft Edge, the browser that will be released after IE11, will only honor the X-UA-Compatible meta tag in certain circumstances. See the Microsoft Edge note below.

According to Microsoft, when using the X-UA-Compatible tag, it should be as high as possible in your documenthead:

If you are using the X-UA-Compatible META tag you want to place it as close to the top of the page’s HEAD as possible. Internet Explorer begins interpreting markup using the latest version. When Internet Explorer encounters the X-UA-Compatible META tag it starts over using the designated version’s engine. This is a performance hit because the browser must stop and restart analyzing the content.

Here are your options:

“IE=edge”

“IE=11”

“IE=EmulateIE11”

“IE=10”

“IE=EmulateIE10”

“IE=9”

“IE=EmulateIE9

“IE=8”

“IE=EmulateIE8”

“IE=7”

“IE=EmulateIE7”

“IE=5”

To attempt to understand what each means, here are definitions provided by Microsoft:

Internet Explorer supports a number of document compatibility modes that enable different features and can affect the way content is displayed:

Edge mode tells Internet Explorer to display content in the highest mode available. With Internet Explorer 9, this is equivalent to IE9 mode. If a future release of Internet Explorer supported a higher compatibility mode, pages set to edge mode would appear in the highest mode supported by that version. Those same pages would still appear in IE9 mode when viewed with Internet Explorer 9. Internet Explorer supports a number of document compatibility modes that enable different features and can affect the way content is displayed:

IE11 mode provides the highest support available for established and emerging industry standards, including the HTML5, CSS3 and others.

IE10 mode provides the highest support available for established and emerging industry standards, including the HTML5, CSS3 and others.

IE9 mode provides the highest support available for established and emerging industry standards, including the HTML5 (Working Draft), W3C Cascading Style Sheets Level 3 Specification (Working Draft), Scalable Vector Graphics (SVG) 1.0 Specification, and others. [Editor Note: IE 9does notsupport CSS3 animations].

IE8 mode supports many established standards, including the W3C Cascading Style Sheets Level 2.1 Specification and the W3C Selectors API; it also provides limited support for the W3C Cascading Style Sheets Level 3 Specification (Working Draft) and other emerging standards.

IE7 mode renders content as if it were displayed in standards mode by Internet Explorer 7, whether or not the page contains a directive.

Emulate IE9 mode tells Internet Explorer to use the directive to determine how to render content. Standards mode directives are displayed in IE9 mode and quirks mode directives are displayed in IE5 mode. Unlike IE9 mode, Emulate IE9 mode respects the directive.

Emulate IE8 mode tells Internet Explorer to use the directive to determine how to render content. Standards mode directives are displayed in IE8 mode and quirks mode directives are displayed in IE5 mode. Unlike IE8 mode, Emulate IE8 mode respects the directive.

Emulate IE7 mode tells Internet Explorer to use the directive to determine how to render content. Standards mode directives are displayed in Internet Explorer 7 standards mode and quirks mode directives are displayed in IE5 mode. Unlike IE7 mode, Emulate IE7 mode respects the directive. For many web sites, this is the preferred compatibility mode.

IE5 mode renders content as if it were displayed in quirks mode by Internet Explorer 7, which is very similar to the way content was displayed in Microsoft Internet Explorer 5.

IE 10 NOTE:As of Internet Explorer 10, quirks mode behaves differently than it did in earlier versions of the browser. In Windows Internet Explorer 9 and earlier versions, quirks mode restricted the webpage to the features supported by Microsoft Internet Explorer 5.5. In Internet Explorer 10, quirks mode conforms to the differences specified in the HTML5 specification.

Personally, I always choose thehttp-equiv="X-UA-Compatible" content="IE=edge"meta tag, as older versions have plenty of bugs, and I do not want IE to decide to go into “Compatibility mode” and show my site as IE7 vs IE8 or 9. I always prefer the latest version of IE.

IE 11

FromMicrosoft:

Starting with IE11, edge mode is the preferred document mode; it represents the highest support for modern standards available to the browser.

Use the HTML5 document type declaration to enable edge mode:

<!doctype html&>

Edge mode was introduced in Internet Explorer 8 and has been available in each subsequent release. Note that the features supported by edge mode are limited to those supported by the specific version of the browser rendering the content.

Starting with IE11, document modes are deprecated and should no longer be used, except on a temporary basis. Make sure to update sites that rely on legacy features and document modes to reflect modern standards.

If you must target a specific document mode so that your site functions while you rework it to support modern standards and features, be aware that you’re using a transitional feature, one that may not be available in future versions.

If you currently use the x-ua-compatible header to target a legacy document mode, it’s possible your site won’t reflect the best experience available with IE11.

Microsoft Edge(Replacement for Internet Explorer that comes bundled with Windows 10)

Information on X-UA-Compatible meta tag for the “Edge” version of IE.From Microsoft:

Introducing the “living” Edge document mode

As we announced in August 2013, we are deprecating document modes as of IE11. With our latest platform updates, the need for legacy document modes is primarily limited to Enterprise legacy web apps. With new architectural changes, these legacy document modes will be isolated from changes in the “living” Edge mode, which will help to guarantee a much higher level of compatibility for customers who depend on those modes and help us move even faster on improvements in Edge. The next major version of IE will still honor document modes served by intranet sites, sites on the Compatibility View list, and when used with Enterprise Mode only.

Public Internet sites will be rendered with the new Edge mode platform (ignoring X-UA-Compatible). It is our goal that Edge is the “living” document mode from here out and no further document modes will be introduced going forward.

With the changes in Microsoft Edge to no longer support document modes in most cases, Microsoft has atool to scan your siteto check and see if it has code that is not compatible with Edge.

Chrome=1 Info for IE

There is alsochrome=1that you can use or use together with one of the above options, EX:<meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1"&>chrome=1is for Google’s Chrome Frame which is defined as:

Google Chrome Frame is an open source browser plug-in. Users who have the plug-in installed have access to Google Chrome’s open web technologies and speedy JavaScript engine when they open pages in the browser.

Google Chrome Frame seamlessly enhances your browsing experience in Internet Explorer. It displays Google Chrome Frame enabled sites using Google Chrome’s rendering technology, giving you access to the latest HTML5 features as well as Google Chrome’s performance and security features without in any way interrupting your usual browser usage.

When Google Chrome Frame is installed, the web just gets better without you having to think about it.

But for that plug-in to work you must usechrome=1in the X-UA-Compatible meta tag.

More info onChrome Frame can be found here.

Note:Google Chrome Frame only works forIE6 through IE9, and was retired on February 25, 2014.More info can be found here. Thank You @mck for the link.

Validation:

HTML5:

The page will validate using theW3 Validatoronly when using<meta http-equiv="X-UA-Compatible" content="IE=Edge"&>. For other values it will throw the error:A meta element with an http-equiv attribute whose value is X-UA-Compatible must have a content attribute with the value IE=edge.In other words, if you haveIE=edge,chrome=1it will not validate. I ignore this error completely as modern browsers simply ignore this line of code.

If you must have completely valid code then consider doing this on the se

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