Comparing two objects that have internal date properties with DateTime objects assigned to them. Why does this work?!

test.php

<?php

class MyTest {
    protected $date;
    public function __construct($time) {
        $this->date = new DateTime($time);
    }
}

$test1 = new MyTest('2013-02-01 00:00:00');
$test2 = new MyTest('2013-03-01 00:00:00');

var_dump($test1 < $test2); // Outputs "true"
var_dump($test1 > $test2); // Outputs "false"