This stack can be used to create a basic, low-security retrieval or login system for a website. The way it works is to cut a standard URL into two parts, with a gap in the middle. It's that 'gap' which forms the input box where a passcode gets typed. So entering a correct passcode in the box completes the URL and forwards a person to a particular folder or file. A wrong passcode redirects a person to an error page. Simple but effective; and ideal to use in lots of situations.