Default Contents

The file.php is the most commonly used plugin. Foreach block level element defined in any layout.xml file, such as:

<div id="footer" src="file" />

...the system will use the plugins/file.php class to generate the footer's content.
For a page whose dynamic URL might be ?page=Driftboats/Beavertail/Online-Plans/index.htm the system will look for a file named footer.frag in the fragments/Driftboats/Beavertail/Online-Plans directory. If that file is found the system will use the php file_get_contents function to supply the needed HTML fragment.

However, if no such file is found the system will fall back on a "default contents" search, by looking in the fragments/hidden directory for the footer's contents. If that file is not found the system uses the null string '' for contents, rather than reporting an error.

So, in other words the developer can use the file.php plugin and file fragments in the fragments/hidden subdirectory for all repeated per-page boilerplate HTML.