Server Side Includes
Server Side Includes are files that have some commonly used code that can be reused by many pages in your site. When you use a SSI file the server takes the entire content of the file and inserts it into the page, replacing the include code. As an example, imagine you have a large portal web site with links at the top, bottom and sides common to all pages (or a section of pages). To make the site easy to maintain you can have the header, footer, right menu and/or left menu as include files. So when there is a change to be made you just need to make the changes, save and upload the corresponding include file and not the many files using it.
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