Apache supports the use of Server Side Includes.
The Apache 1.2 Documentation contains instruction for using server-side includes in your documents.
We use the XBITHACK method for indicating to the server which documents might contain includes. This means that if you make your .html documents executable with the command
chmod +x filename.html the server will parse them looking for Server-Side include commands. This differs from some other systems which require you to rename your documents to .shtml.