 <p>From the <a href="http://docs.jquery.com/Is" rel="nofollow">jQuery documentation for <code>is</code></a>.</p> <blockquote> <p>Checks the current selection against an expression and returns true, if at least one element of the selection fits the given expression.</p> <p>If no element fits, or the expression is not valid, then the response will be 'false'.</p> </blockquote> <p>So you can be sure the answer will either be <code>true</code> or <code>false</code>.</p>