Representation of date period.
Exclude start date, used in DatePeriod::__construct().
Nice example from PHP Spring Conference (thanks to Johannes Schlüter and David Zülke)
<?php
$begin = new DateTime( '2007-12-31' );
$end = new DateTime( '2009-12-31 23:59:59' );
$interval = DateInterval::createFromDateString('last thursday of next month');
$period = new DatePeriod($begin, $interval, $end, DatePeriod::EXCLUDE_START_DATE);
foreach ( $period as $dt )
echo $dt->format( "l Y-m-d H:i:s\n" );
?>
DateInterval specs could be found at http://en.wikipedia.org/wiki/ISO_8601#Time_intervals