Showing and hiding conditional HTML without Javascript

Have you ever filled out an address form that had a checkbox for “my shipping address differs from my mailing address”? When you click that box a conditional form part gets revealed that allows you to enter another address. We had to build something very similar the other day and stumbled on a neat way to make the conditional part show and hide with CSS only.

Here is how:
http://pivotallabs.com/conditional-html-forms-without-javascript/