public static function get_primary_accept() {
	if (empty($_SERVER['HTTP_ACCEPT'])) {
		return '*';
	}
	
	// catch the most common formats
	if (strpos($_SERVER['HTTP_ACCEPT'], 'text/html,') === 0) {
		return 'html';
	}
	if (strpos($_SERVER['HTTP_ACCEPT'], 'application/json,') === 0) {
		return 'json';
	}
	
	// use a generic method
	return self::get_primary_mime_type($_SERVER['HTTP_ACCEPT']);
}