It's useful to note (and it should be obvious) that while the documentation says that \DateTimeImmutable should act just like a \DateTime object. That is true, until you use instanceof.
\DateTimeImmutable is not an instance of \DateTime
(PHP 5 >= 5.5.0)
This class behaves the same as DateTime except it never modifies itself but returns a new object instead.
$day= 1 ] )
$second= 0 ] )