- var_dump: documentation ( source)
<?php
$string = '2018-01-11T15:36:16.000+01:00';
$datetime = new \DateTimeImmutable($string);
var_dump(
$datetime->format(\DateTime::RFC3339_EXTENDED) === $string,
\DateTimeImmutable::createFromFormat(\DateTime::RFC3339_EXTENDED, $string),
\DateTimeImmutable::getLastErrors()
);