Regular expression for youtube url
<p>what is the regular expression for a url ? 
in my web application i want to validate url when the user enters the url in textbox.</p>

<p>url like: <a href="http://www.youtube.com/embed/OWj0fns95xw" rel="nofollow">http://www.youtube.com/embed/OWj0fns95xw</a></p>
