public function calendarTimeZone()
{
$default_timezone = date_default_timezone_get();
if (isset($this->cal['VCALENDAR']['X-WR-TIMEZONE'])) {
$timezone = $this->cal['VCALENDAR']['X-WR-TIMEZONE'];
} else {
if (isset($this->cal['VTIMEZONE']['TZID'])) {
$timezone = $this->cal['VTIMEZONE']['TZID'];
} else {
return $default_timezone;
}
}
// Use default timezone if defined is invalid
if (!$this->isValidTimeZoneId($timezone)) {
return $default_timezone;
}
return $timezone;
}