public static function load_class( $class_name = NULL ) {

		// if spl_autoload_register not exist
		if ( NULL === $class_name ) {
			// load required classes
			foreach ( glob( dirname( __FILE__ ) . '/*.php' ) as $path ) {
				require_once $path;
			}
		} else {
			if ( 0 !== strpos( $class_name, 'Iac_' ) )
				return FALSE;

			// if param have a class string
			$path = dirname( __FILE__ ) . '/class-' . $class_name . '.php';
			if ( file_exists( $path ) ) {
				require_once $path;

				return TRUE;
			}
		}

		return FALSE;
	}