The Ajas HashHistory class is useful for helping the browser's history to keep up with activities between page requests. It essentially 'unbreaks' the Back and Forward history buttons in 'AJAX' applications. The class also aids 'Deep Linking' in 'AJAX' applications. By responding the the hash part of the URL, a specified callback function can set the page to the intended state. Test this by clicking one of the four number-named links below, or, by setting the hash part of the URL manually, then by pressing the browser's back and forward buttons.