How to detect the position of an element changed?
<p>Consider the situation where <strong>div-A</strong> has a relative position to <strong>div-B</strong> (actually,<strong>div-A</strong> is hovering over <strong>div-B</strong> by different <strong>Z-Index</strong>). When the position of <strong>div-B</strong> changes, <strong>div-C</strong> is to be inserted before it and <strong>div-A</strong> is to be hidden.</p>

<p>The question is: how to detect the position changing of <strong>div-B</strong>?</p>
