Apache Reference: mod_include
mod_include - Server-Side Includes (SSI) Implementation
Since Apache 1.0, src/modules/standard/mod_include.c
The Apache Group (1995)
mod_include implements an extended version of the Server-Side Includes (SSI) quasi-standard, (which was originally introduced by the NCSA httpd). Embedded programming constructs in a HTML document are evaluated "on the fly" and expanded by the server before the document is sent to the client. The name of the module relates to a major goal of SSI --- its role as a file inclusion facility. But it should be not neglected that using this facility decreases server performance.