private function buildChildrenErrors(array $childrenErrors, $msg)
    {
        if (!empty($childrenErrors)) {
            $msg .= PHP_EOL.'- children:';

            foreach ($childrenErrors as $child => $errors) {
                $msg .= sprintf('%s  - %s', PHP_EOL, $child);
                $msg .= sprintf('%s    - errors:', PHP_EOL);

                foreach ($errors as $error) {
                    $msg .= sprintf('%s      - %s', PHP_EOL, $error);
                }
            }
        }

        return $msg;
    }