A solid foundation in the core fundamentals leaves the student ready to apply this knowledge in diverse environments.  The text emphasizes that central concepts are more important than the implementation of a particular language; however, Perl is used as the server-side language because of its portability, its highly developed code libraries, and its widespread use in the development of web applications worldwide.  Moreover, the use of Perl enabled the authors to expose the central concepts, sometimes obscured by environments, proprietary or otherwise, which were created solely as tools for web programming. Alternate languages, PHP and ASP are covered in supplementary online Web Extension chapters.