<meta http-equiv="X-UA-Compatible" content="IE=edge"> error in W3C validation

Question

I am using Bootstrap 3.

When I add <meta http-equiv="X-UA-Compatible" content="IE=edge">, the site shows error in the W3C validator.

Answer 1

You can do:

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

Answer 2

From my answer to a similar question:

In (X)HTML5, you may only use http-equiv values that are

• defined in the HTML5 spec, or
• registered in the WHATWG wiki page "PragmaExtensions".

The value X-UA-Compatible is not defined in the spec, but it’s proposed in the wiki. "Proposed" means:

The following proposed extensions do not yet conform to all the registration requirements in the HTML spec and are therefore not yet allowed in valid documents.

So currently it’s not valid to use this value in (X)HTML5.

Answer 3

The validator is extremely pedantic. It's best to just ignore this particular validation warning, given its significant pragmatic benefit and complete lack of downsides. It's not an error of any kind in any of the major browsers.