X-UA-Compatibility with HTTP Header

Question

actually i'm having a problem with a website in IE which is not on intranet and the "always show pages in compatibility mode is not activated" but it still opens in quirks mode sometimes, despite adding

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

I have red that i can send this compatibility order in an HTTP Header or in htaccess

My problem is that i have searched on how to send an HTTP header and actually found no clue, and btw i'm a php developer just in case this information was necessary.

I would really appreciate if someone could provide me what's needed to add (for both, or for one at least) and how/where to add it, i have been looking for the whole week and it's quiet urgent to find the fix so soon !

Is this way to send it as an HTTP header as a first line in the page is right ?

<?php
header('X-UA-Compatible: IE=edge');
?>

(I have just found it)

I really appreciate any help can be provided and i'm thankful in advance.

Answer 1

As you correctly noted the header can be set in php:

<?php header('X-UA-Compatible: IE=edge,chrome=1');

It can also be set in .htaccess like so:

<IfModule mod_headers.c>
  Header set X-UA-Compatible "IE=Edge,chrome=1"
  # mod_headers can't match by content-type, but we don't want to send this header on *everything*...
  <FilesMatch "\.(appcache|crx|css|eot|gif|htc|ico|jpe?g|js|m4a|m4v|manifest|mp4|oex|oga|ogg|ogv|otf|pdf|png|safariextz|svg|svgz|ttf|vcf|webm|webp|woff|xml|xpi)$">
    Header unset X-UA-Compatible
  </FilesMatch>
</IfModule>

(copied from the HTML5 Boilerplate template)

However, if you are setting these headers and finding that IE still defaults to quirks-mode then I'd be inclined to suggest that there is something else at work. Have you ensured that your pages include a valid doctype? Notably one that isn't of the HTML 4.01 flavour.