supported by Apache HTTPd's `mod_include`:
http://web.archive.org/web/19971210170837/http://hoohoo.ncsa.uiuc.edu/docs/tutorials/includes.html
- http://httpd.apache.org/docs/current/mod/mod_include.html
+ http://httpd.apache.org/docs/2.2/mod/mod_include.html
ssic uses the `CGI::SSI` Perl module for directive processing.