What is it?
Server Side Includes are directives to the server to include addtional information or to specifify formats.
All directives to the server are formatted as SGML comments within the document.
This is in case the document should ever find itself in the client's hands
unparsed. Each directive has the following format:
<!--#command tag1="value1" tag2="value2" -->
Each command takes different arguments, most only accept one tag at a time.