silverstripe-framework/admin/code/LeftAndMainExtension.php

<?php
/**
 * Plug-ins for additional functionality in your LeftAndMain classes.
 * 
 * @package    cms
 * @subpackage core
 */
abstract class LeftAndMainExtension extends Extension {

	public function init() {
	}
	
	public function accessedCMS() {
	}
	
	public function augmentNewSiteTreeItem(&$item) {
	}

}