$modeString = (isset($_GET['mode']) && strtolower($_GET['mode']) === 'string');
if ($modeString) {
    header('Content-Type: text/plain; charset=utf-8');
    echo "Nombre d'événements : " . count($occurrences);
    exit;
}
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//NeoCraft1293//Stream Planner//FR
X-WR-CALNAME:NeoCraft Stream
X-WR-TIMEZONE:Europe/Paris
END:VCALENDAR