Clarification about the order of variables used in a function
<p>I've been fighting with this PHP-snippet for some hours and I can't figure it out...<br>
How does PHP determines the order when to pass the variables in this snippet:</p>

<pre><code>function myfunction ($left, $right) {
    echo $left;
    echo '&lt;br&gt;';
    echo $right;

}

$a = array ('one', 'two', 'three', 'four');

usort($a, 'myfunction');
</code></pre>

<p>In this case, the variables are passed like this:</p>

<pre><code>$left = 'two'   - $right = 'one';
$left = 'four'  - $right = 'two';
$left = 'three' - $right = 'two';
$left = 'four'  - $right = 'three';
</code></pre>

<p>But how is this sequence determined?!? I've been cracking my head and couldn't find any logic... </p>
