That's because SSI is a server-side technology that leaves no fingerprints in the resulting Web page. When the Web server gets a request for a page containing SSIs, it scans every line of the HTML source for SSI statements. When it finds one, it inserts the included file into the HTML source, removing the SSI statement in the process. To see the source code of our basic page as it really resides on the Web server, click here . This shows you what the file looks like before server parsing.
Server parsing is an important point to remember about SSIs.
If you build a page using SSIs on your desktop computer, the SSI statements won't work. You won't see the results of your SSI until you upload the pages to your Web server. Like CGI scripts, SSIs require some special server configuration before they are enabled. You may need to contact your ISP or Web hosting service and let them know that you'd like to use SSIs in your site. That file extension tells the Web server that this file includes SSIs.