Restrict by continent:
<?php
$ids = timezone_identifiers_list( DateTimeZone::EUROPE );
echo implode( ", ", $ids );
?>
Output
Europe/Amsterdam, Europe/Andorra, Europe/Astrakhan, Europe/Athens, Europe/Belgrade, Europe/Berlin, Europe/Bratislava, Europe/Brussels, Europe/Bucharest, Europe/Budapest, Europe/Busingen, Europe/Chisinau, Europe/Copenhagen, Europe/Dublin, Europe/Gibraltar, Europe/Guernsey, Europe/Helsinki, Europe/Isle_of_Man, Europe/Istanbul, Europe/Jersey, Europe/Kaliningrad, Europe/Kirov, Europe/Kyiv, Europe/Lisbon, Europe/Ljubljana, Europe/London, Europe/Luxembourg, Europe/Madrid, Europe/Malta, Europe/Mariehamn, Europe/Minsk, Europe/Monaco, Europe/Moscow, Europe/Oslo, Europe/Paris, Europe/Podgorica, Europe/Prague, Europe/Riga, Europe/Rome, Europe/Samara, Europe/San_Marino, Europe/Sarajevo, Europe/Saratov, Europe/Simferopol, Europe/Skopje, Europe/Sofia, Europe/Stockholm, Europe/Tallinn, Europe/Tirane, Europe/Ulyanovsk, Europe/Vaduz, Europe/Vatican, Europe/Vienna, Europe/Vilnius, Europe/Volgograd, Europe/Warsaw, Europe/Zagreb, Europe/Zurich
Restrict by country:
<?php
$ids = timezone_identifiers_list( DateTimeZone::PER_COUNTRY, 'CA' );
echo implode( ", ", $ids );
?>
Output
America/Atikokan, America/Blanc-Sablon, America/Cambridge_Bay, America/Creston, America/Dawson, America/Dawson_Creek, America/Edmonton, America/Fort_Nelson, America/Glace_Bay, America/Goose_Bay, America/Halifax, America/Inuvik, America/Iqaluit, America/Moncton, America/Rankin_Inlet, America/Regina, America/Resolute, America/St_Johns, America/Swift_Current, America/Toronto, America/Vancouver, America/Whitehorse, America/Winnipeg