Warning - despite the $interval_spec accepting the ISO 8601 specification format, it does not accept decimal fraction values with period or comma as stated in the specification.
https://bugs.php.net/bug.php?id=53831
<?php
/* Example from ISO 8601 documentation */
$interval = new DateInterval('P0.5Y');
?>
Will result in
Fatal error: Uncaught exception 'Exception' with message 'DateInterval::__construct(): Unknown or bad format (P0.5Y)'