public static function debug(array $strings, array $placeholders = [])
    {
        // Initialize messages storage.
        if (!isset($_SESSION[__TRAIT__])) {
            $_SESSION[__TRAIT__] = [];
        }

        // Mark debug message.
        array_unshift($strings, '<question>DEBUG:</question>');

        $_SESSION[__TRAIT__][] = new Message('comment', 4, $strings, $placeholders, (bool) getenv('BEHAT_DEBUG'));
    }