window.historyobject, which is necessary for back links:
Generally speaking a back link isn't necessary… the Back button usually suffices quite nicely, and usually you can also simply link to the previous page in your site. However, sometimes you might want to provide a link back to one of several "previous" pages, and that's where a back link comes in handy.
The following pages shows you how to implement a simple, flexible back link script without many of the problems inherent in this type of scripting. We'll begin with the
basic technique, then move on to ways to customize your backlink.