I created the backbone structure for the site in XHTML 1.1 (Extensible HyperText Markup Language). Nearly all of the pages use server side includes (SSI), meaning that (usually small) files containing content for display are inserted at run time. This facilitates updating since the same content, such as my postal address, may be needed in several locations on the site. The use of SSI's is the explanation for the .shtml extension on many of the files.