What does this mean? $length = null === $length ? strlen($data) : (int)$length ;
<p>I'm aware of ternary operator, more or less. 
But I'm unable to read this line.</p>

<pre><code>$length = null === $length ? strlen($data) : (int)$length ;
</code></pre>

<p>What does $length = null === $length means?</p>

<p>Thanks a lot,
MEM</p>
