What is X-UA compatible when it refers to IE = edge, chrome = 1?

Question

I just saw this meta tag in the wild and wondered what it does and why it used.

<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" /> 

Reading the documentation on About.com, he says:

"IE = edge" tells Internet Explorer to use the highest mode available for this version of IE. Internet Explorer 8 supports up to IE8 modes, IE9 can support IE9 modes, etc.

But what about the chrome=1 tag?

Answer 1

This is a Google Chrome Frame app.

ChromeFrame can be installed in various versions of IE (especially useful for older versions that do not play well with modern web features). It essentially launches the Chrome browser in IE.

In the case of a meta tag, IE should start in standards mode (most modern editions of Edge) and activate chromatic frames, if one exists.

I usually do some conditional browser stuff for older versions of IE, allowing the user to set the add-in as an option.

More info here: chrome frame API

(Keep in mind that Google Chrome Frame is no longer supported)

Answer 2

In addition, starting with the "edge" mode of IE11, which used to be experimental, is now the "preferred" mode - see Compatibility Changes in IE11 Preview

In addition, “document modes” usually become obsolete in IE11 all together, so you should probably stop there depending on them.