public function yesCacheSend(int $expires_after = self::SECONDS_IN_YEAR)
    {
        if (headers_sent()) {
            throw $this->c::issue('Headers already sent.');
        }
        header_remove('last-modified');

        foreach ($this->yesCache() as $_header => $_value) {
            header($_header.': '.$_value);
        } // unset($_header, $_value);
    }