protected function checkIfSysFoldersOrEmpty(
        $fieldName,
        $canUseFlexforms,
        $sheet,
        $explanation
    ) {
        $pids = $this->objectToCheck->getConfValueString($fieldName, $sheet);

        // Uses the plural if the configuration value is empty or contains a
        // comma.
        if (($pids === '') || (strrpos($pids, ',') !== false)) {
            $message = 'All the selected pages need to be system folders so '
                . 'that data records are tidily separated from front-end '
                . 'content. ' . $explanation;
        } else {
            $message = 'The selected page needs to be a system folder so that '
                . 'data records are tidily separated from front-end content. '
                . $explanation;
        }
        $this->checkPageTypeOrEmpty(
            $fieldName,
            $canUseFlexforms,
            $sheet,
            $message,
            '=254'
        );
    }