<?php
ini_set('date.timezone', 'Europe/Lisbon');
ini_set('intl.default_locale', 'pt_PT');
$cal = new IntlGregorianCalendar(2013, 5 /* June */, 30);
$cal->add(IntlCalendar::FIELD_DAY_OF_MONTH, 1);
var_dump(IntlDateFormatter::formatObject($cal)); // "01/07/2013, 00:00:00"
$cal->set(2013, 5 /* June */, 30);
$cal->roll(IntlCalendar::FIELD_DAY_OF_MONTH, true); // roll up, same as rolling +1
var_dump(IntlDateFormatter::formatObject($cal)); // "01/06/2013, 00:00:00"
string(20) "01/07/2013, 00:00:00"
string(20) "01/06/2013, 00:00:00"