not understood working js code
<p>Please see this:
<a href="http://jsfiddle.net/Muj3d/8/" rel="nofollow">http://jsfiddle.net/Muj3d/8/</a></p>

<p>suppose mouse cursor is on <code>div_1</code>, now drag mouse from <code>div_1</code> to <code>div_2</code>, as we see, first time happened action <code>mouseout</code> and after <code>mouseover</code>. Ok, now remove <code>alerts()</code> from js code and repeat mouse drag again, as we see, <code>div_2</code> not removed, question: why?</p>
