How do you create a jQuery plugin?
<p>I have the following code, which I am following from the jQuery documentation on how to build a plugin.</p>

<p>I'm just trying to create a simple isNot extension:</p>

<pre><code>(function ($) {
    $.fn.isNot = function (selector) {
        return !this.is(selector);
    };
})(jQuery);

$(document).ready(function () {
    $("#someButton").click(function (event) {
        alert($("#someCheckbox").isNot(":checked"));           
    });
});
</code></pre>

<p>When I run this the javascript file get's loaded properly, and I can step through the code in firebug. I see that jQuery is defined properly, and the click event gets wired up properly, too.</p>

<p>However, I have added a watch in FireBug to track the isNot function, and it is <strong>always</strong> null.  I can't get it to ever become defined.</p>

<p>Is there something I'm not doing properly?</p>
