simple jQuery addition
<p>Why does</p>

<pre><code>$(this).css("z-index") + 10;
</code></pre>

<p>not add 10 to the amount?</p>

<p>The result I'm getting is <code>1010</code>, while I'm expecting to get <code>20</code>.</p>

<p>I thought it would need to be in quotes for it to do that.</p>
