What useful custom jQuery selectors have you written?

Question

For me, one of the best, yet under-utilised feature of jQuery is the custom selector. I have a fairly trivial example of this, to pick out all text boxes that are empty:

Answer 1

As custom selectors are suggested on stackoverflow I'll add them here

Select 'URL' style

Selecting empty text input using jQuery

Answer 2

If you are using ASP.NET, this selector will help you find server controls by id:

$.expr[":"].asp = function(a, i, m) {
    return $(a).attr('id') && $(a).attr('id').endsWith(m[3]);
};

If you had a server control that looked like

<asp:TextBox runat="server" ID="txtPhoneNumber" />

You could access it like this

$(":asp(txtPhoneNumber)")

EDIT

Forgot to add the endsWith extension

String.prototype.endsWith = function(str) {
    return (this.match(str + '$') == str);
};

Answer 3

I haven't written any, yet James Padolsey has a great collection of selector plug-ins (for elements in view, for external links, for elements with a specific .data property, etc)