public function toHex($prefixHexContent = false)
    {
        $chars = $this->getPlain();
        if ($prefixHexContent && ctype_xdigit($chars)) {
            return "fe" . $chars;
        }

        $payload = "";
        for ($c = 0, $cnt = strlen($chars); $c < $cnt; $c++ ) {
            $decimal = ord($chars[$c]);
            $hexCode = dechex($decimal);

            // payload is built of *hexits*
            $payload .= str_pad($hexCode, 2, "0", STR_PAD_LEFT);
        }

        $this->payload = strtolower($payload);
        return $this->payload;
    }