Description:
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From manual page: http://www.php.net/datetimeimmutable.createfromformat
---

According to the manual (and the common sense also), 
DateTimeImmutable::createFromFormat should return a DateTimeImmutable object, but 
instead of that it returns a DateTime one.

Test script:
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I've used the CLI console to test it:

php > $today = DateTimeImmutable::createFromFormat('Y-m-d|', '2013-08-22');
php > $tomorrow = $today->add(new DateInterval('P1D'));
php > var_dump($today->format('Y-m-d'), $tomorrow->format('Y-m-d'));
string(10) "2013-08-23"
string(10) "2013-08-23"
php > var_dump($today instanceof DateTimeImmutable);
bool(false)
php > var_dump($today instanceof DateTime);
bool(true)

Expected result:
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$today must contain a DateTimeImmutable object and thus it must be immutable.

Actual result:
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$today is a DateTime object instead of DateTimeImmutable