Why does datetime->days always returns a positive number
<pre><code>$today = new DateTime();
$date = new DateTime('2013-03-10');
$interval = $date-&gt;diff($today);
return $interval-&gt;days;
// returns 4


$today = new DateTime();
$date = new DateTime('2013-03-10');
$interval = $today-&gt;diff($date); // arguments swapped around here
return $interval-&gt;days;
// returns 4
</code></pre>

<p>Why do both of these functions return positive 4? How do I return a negative number if $date is in the past?</p>
