What does “P” mean in DateInterval format?

Question

Consider the following example given in php manual for DateTime

<?php $date = new DateTime('2000-01-20'); $date->sub(new DateInterval('P10D')); echo $date->format('Ym-d') . "\n"; ?> 

'D' for a few days, what does the “P” mean in this formatting?

Answer 1

From the manual

Interval specification.

The format starts with the letter P for "period". Each duration period is represented by an integer value followed by a period indicator. If the duration contains time elements, that part of the specification is preceded by the letter T.

Answer 2

'P' means Period. see here http://php.net/manual/en/dateinterval.construct.php