WordPress X-UA-Compatible Headers for IE

setup.php

/**
 * Set X-UA-Compatible for IE
 *
 * Sends headers to browser in an attempt to have IE render the website using
 * their latest rendering engine (i.e. IE=edge). Additionally, attempts to
 * activate Chrome Frame add-on if it exists.
 *
 * IE browser may show compatibility icon in address bar when using HTML5 Boilerplate's
 * heading markup which contains conditional comments on HTML tag.
 *
 * Setting the X-UA-Compatible meta tag will not work if placed after the HTML
 * conditional comments.
 *
 * While there are workarounds, the preferred method is to send headers, not markup.
 *
 * IE should attempt to render website using its "stable" engine. I believe as
 * of IE10, this is edge.
 *
 * @link Explanation of values: http://stackoverflow.com/a/14637972/3163972
 * @link Solution: http://stackoverflow.com/a/9624500/3163972
 * @link HTML5 Boilerplate's Take: https://github.com/h5bp/html5-boilerplate/issues/378
 * @link Reasons Compatibility Mode may be set: http://stackoverflow.com/a/3726605/3163972
 */
function prefix_add_header_xua() {

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

}
add_action( 'send_headers', 'prefix_add_header_xua' );