silverstripe-framework/admin/code/LeftAndMainExtension.php

<?php

namespace SilverStripe\Admin;

use SilverStripe\Core\Extension;

/**
 * Plug-ins for additional functionality in your LeftAndMain classes.
 */
abstract class LeftAndMainExtension extends Extension {

	public function init() {
	}

	public function accessedCMS() {
	}

	public function augmentNewSiteTreeItem(&$item) {
	}

}