public function getBarcodeSVG($w = 2, $h = 30, $color = 'black')
{
// send headers
$code = $this->getBarcodeSVGcode($w, $h, $color);
header('Content-Type: application/svg+xml');
header('Cache-Control: public, must-revalidate, max-age=0');
// HTTP/1.1
header('Pragma: public');
header('Expires: Sat, 26 Jul 1997 05:00:00 GMT');
// Date in the past
header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . ' GMT');
header('Content-Disposition: inline; filename="' . md5($code) . '.svg";');
//header('Content-Length: '.strlen($code));
echo $code;
}