Contao\Controller::isVisibleElement PHP Method

    public static function isVisibleElement(Model $objElement)
    {
        $blnReturn = true;
        // Only apply the restrictions in the front end
        if (TL_MODE == 'FE') {
            // Protected element
            if ($objElement->protected) {
                if (!FE_USER_LOGGED_IN) {
                    $blnReturn = false;
                } else {
                    $groups = \StringUtil::deserialize($objElement->groups);
                    if (empty($groups) || !is_array($groups) || !count(array_intersect($groups, \FrontendUser::getInstance()->groups))) {
                        $blnReturn = false;
                    }
                }
            } elseif ($objElement->guests && FE_USER_LOGGED_IN) {
                $blnReturn = false;
            }
        }
        // HOOK: add custom logic
        if (isset($GLOBALS['TL_HOOKS']['isVisibleElement']) && is_array($GLOBALS['TL_HOOKS']['isVisibleElement'])) {
            foreach ($GLOBALS['TL_HOOKS']['isVisibleElement'] as $callback) {
                $blnReturn = static::importStatic($callback[0])->{$callback[1]}($objElement, $blnReturn);
            }
        }
        return $blnReturn;
    }