How to add alphanumeric validation to jQuery validation plugin?

This exact question was asked here:

using the jquery validation plugin, how can I add regular expression validation to a text box?

But unfortunately, the solution does not work for me. I use the very popular jquery validation plugin, in particular this version:

http://jquery.bassistance.de/validate/jquery.validate.js

I tried to add a custom alphanumeric function (from the above stack overflow question):

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
<script type="text/javascript" src="http://jquery.bassistance.de/validate/jquery.validate.js"></script>

<script type="text/javascript">
$(function() {

    $.validator.addMethod("loginRegex", function(value, element) {
        return this.optional(element) || /^[a-z0-9\-]+$/i.test(value);
    }, "Username must contain only letters, numbers, or dashes.");

    $("#myForm").validate({
        rules: {
            "login": {
                required: true,
                loginRegex: true,
            }
        },
        messages: {
            "login": {
                required: "You must enter a login name",
                loginRegex: "Login format not valid"
            }
        }
    });

});
</script>

<form method="post" id="myForm">
    <input type="text" name="login" />  
    <input type="submit" value="Go" />  
</form>

If you run this code, you will see that it only checks for the presence of some type of input, it does not check the input through a custom alphanumeric function. How can this be made to work?