# Chapter 7. eXtended Server Side Includes

# What are XSSI?

XSSI (eXtended Server Side Includes) are a set of directives that can be put in a HTML page and interpreted by the web server while it sends the page to a client. You can use XSSI to insert in your HTML page:

- The value of an environment variable.

- The size and the last modification time of a file.

- A file.

- The output of a script or a shell command.

XSSI also supports conditional processing as well as declaring variables and setting their values.