Server-side includes (SSI) tell a server to include information in a document before sending it to the browser. All directives to the server are formatted as SGML comments within the document. In case the document should find its way to the client unparsed
, it will harmlessly remain unrendered. Each server-side include is written in the format
!--#command tag1="value1" tag2="value2" --
. The simplest kind of SSI is a virtual include, which can use one command to pull HTML fragments, such as navigation bars, into all the pages of a site without having to hand code each page.
(see eXtended Server-Side Includes)