Server Side Includes (SSI) are a simple component system that, when enabled, instructs the web server to parse the html components in a top-to-bottom fashion as they are served. The parser scans for tags that look a lot like HTML comments. In fact, if you have SSI tags embedded in the page without the server side parsing enabled, your HTML will be served with a bunch of HTML comments visible when you "View Source." However, when the parser is enabled, each SSI is replaced with something else such as the contents of another file or virtual content, a variable value or a formatted date.

It's unlikely that we'll ever see a SAMS Press book titled "Teach Yourself SSI's in 24 Hours" -- there's just not that much to it. And yet questions about the capabilities of SSI's arise from time to time. Thus, I've prepared this mini-tutorial.