protected function listCalcDepth($pageUid, array $rootLineRaw, $depth = null)
    {
        if ($depth === null) {
            $depth = 1;
        }

        if (empty($rootLineRaw[$pageUid])) {
            // found root page
            return $depth;
        }

        // we must be at least in the first depth
        ++$depth;

        $pagePid = $rootLineRaw[$pageUid];

        if (!empty($pagePid)) {
            // recursive
            $depth = $this->listCalcDepth($pagePid, $rootLineRaw, $depth);
        }

        return $depth;
    }