regular expression formatting

Hi experts,

I saw this example that uses the jQuery Validation plugin and jQuery masked input plugin

http://jsfiddle.net/2hdTn/

In this example this custom validation method is used for United States phone number format which looks like this:

(123) 123-1234 x123456


jQuery.validator.addMethod("usPhoneFormat", function (value, element) {
    return this.optional(element) || /^\(\d{3}\) \d{3}\-\d{4}( x\d{1,6})?$/.test(value);
}, "Enter a valid phone number.");

this examples uses a mask like this for that us phone number

$(".phone").mask("?(999) 999-9999 x999999");

I'm tried to redo this example for a social security number format.

So my mask is like this $(".ssn").mask("###-##-####");

I'm having trouble writing the regular expression for a social security number format in my custom validation method.

Anyone know what  the syntax for my regular express in my method should be for a social format that looks like this:  123-45-6789  

So far I have this:

jQuery.validator.addMethod("SocialNumberFormat", function (value, element) {
    return this.optional(element) || /^\(\d{3}\) \d{3}\-\d{4}( x\d{1,6})?$/.test(value);
}, "Enter a valid social");