PHP | DatePeriod getStartDate() Function

<?php

// Initialising a startDate with time
$StartDate = new DateTime('2019-05-16T00:00:00Z');

// Initialising a DateInterval of 2 day
$DateInterval = new DateInterval('P2D');

// Initialising a endDate with time
$EndDate = new DateTime('2019-05-20T00:00:00Z');

// Initialising a DatePeriod with startDate, DateInterval and
// endDate 
$datePeriod = new DatePeriod( $StartDate, $DateInterval, $EndDate);
    
// Calling the getStartDate() function
$StartDate = $datePeriod->getStartDate();

// Getting the start date
echo $StartDate->format(DateTime::ISO8601);

?>

<?php

// Initialising a DatePeriod with a date of 2019-09-30,
// time of 10 hours, 40 minutes and 44 seconds and with
// day period of 14 days
$datePeriod = new DatePeriod('R7/2019-09-30T10:40:44Z/P14D');
    
// Calling the getStartDate() function
$StartDate = $datePeriod->getStartDate();

// Getting the start date
echo $StartDate->format(DateTime::ISO8601);
?>