Source

File: wp-includes/functions.php

function iis7_supports_permalinks() {
	global $is_iis7;

	$supports_permalinks = false;
	if ( $is_iis7 ) {
		/* First we check if the DOMDocument class exists. If it does not exist, then we cannot
		 * easily update the xml configuration file, hence we just bail out and tell user that
		 * pretty permalinks cannot be used.
		 *
		 * Next we check if the URL Rewrite Module 1.1 is loaded and enabled for the web site. When
		 * URL Rewrite 1.1 is loaded it always sets a server variable called 'IIS_UrlRewriteModule'.
		 * Lastly we make sure that PHP is running via FastCGI. This is important because if it runs
		 * via ISAPI then pretty permalinks will not work.
		 */
		$supports_permalinks = class_exists( 'DOMDocument', false ) && isset( $_SERVER['IIS_UrlRewriteModule'] ) && ( 'cgi-fcgi' === PHP_SAPI );
	}

	/**
	 * Filters whether IIS 7+ supports pretty permalinks.
	 *
	 * @since 2.8.0
	 *
	 * @param bool $supports_permalinks Whether IIS7 supports permalinks. Default false.
	 */
	return apply_filters( 'iis7_supports_permalinks', $supports_permalinks );
}