private function formatTimestamp($timestamp, $format)
{
if (strncmp($format, 'php:', 4) === 0) {
$format = substr($format, 4);
} else {
$format = FormatConverter::convertDateIcuToPhp($format, 'date');
}
$date = new DateTime();
$date->setTimestamp($timestamp);
$date->setTimezone(new \DateTimeZone($this->timestampAttributeTimeZone));
return $date->format($format);
}