The HTML Pre-Processor is a perl5 script that does basic including, #defines, and assertions for HTML, much like cpp(1) does for .c source files, but it is lacking a lot of cpp's features (and internal complexity). HPP is useful for simple site includes and conditionals on sites that do not have SSI or where its useful to have pages "pre-compiled", and may be useful just to do a unified look n feel throughout your pages.
