"Server-side includes (SSI) provide a means to add dynamic content to existing HTML documents," according to the Apache SSI tutorial. "SSI is certainly not a replacement for CGI, or other technologies used for generating dynamic web pages. But it is a great way to add small amounts of dynamic content to pages, without doing a lot of extra work."

If the web server sees certain instructions hidden inside HTML comments, the server executes those instructions. The server is configured to only process SSI instructions in files ending in .shtml.

We demonstrate a few SSI tricks on our SSI demo page.

We disabled SSI features that enable people to run arbitrary programs on the web server (such as exec) on the grounds that they create a dangerous system vulnerability.

References

1. https://en.wikipedia.org/wiki/Server_Side_Includes
2. httpd.apache.org/docs/2.2/howto/ssi.html
3. SSI demo page