For this tutorial, consider a requirement to prevent cross-linking of content on your website from some other website. A typical situation in which this might be useful is where your website contains some graphical content that some other website includes in its own web pages. Every time someone views the other web page, it causes a hit on your own web server, wasting valuable bandwidth and system resources.
Note that it is assumed that you are familiar with CGI variables and how to use them to examine certain properties of a web request. In this tutorial, you will use the following CGI variables: