Periodically check an element of a web page
<p>How to implement a web service that periodically checks if an element of a web page (say, <code>&lt;div id="contentlist"&gt;</code>) has changed; then if there is a change, send a notification to an email address?</p>

<p><strong>Update</strong></p>

<p>There is one issue. The web page is dynamically generated, so if I look at the HTML source, there is nothing in the targe element.</p>

<p>And I want to implement this as a web service. Can I do that in cron?</p>
