This file is just an example of simply XHTML. If any of the HTML source in this file is at all unfamiliar you should take the time to look at the HTML tutorial before going any further with PHP.
The extension to this text file may be .php, but it is interpreted as if it had an .HTML extension! All the browser receives is the HTML streaming from this file. The HTML may also include client-side javascript and stylesheets.
The javascript file referenced in the head of this document defines the followUp function that is used by the button below