Source

File: wp-admin/includes/misc.php

function iis7_save_url_rewrite_rules() {
	if ( is_multisite() ) {
		return;
	}

	global $wp_rewrite;

	// Ensure get_home_path() is declared.
	require_once ABSPATH . 'wp-admin/includes/file.php';

	$home_path       = get_home_path();
	$web_config_file = $home_path . 'web.config';

	// Using win_is_writable() instead of is_writable() because of a bug in Windows PHP.
	if ( iis7_supports_permalinks() && ( ( ! file_exists( $web_config_file ) && win_is_writable( $home_path ) && $wp_rewrite->using_mod_rewrite_permalinks() ) || win_is_writable( $web_config_file ) ) ) {
		$rule = $wp_rewrite->iis7_url_rewrite_rules( false );
		if ( ! empty( $rule ) ) {
			return iis7_add_rewrite_rule( $web_config_file, $rule );
		} else {
			return iis7_delete_rewrite_rule( $web_config_file );
		}
	}
	return false;
}