private function myCombineDirectoryPart(string $part, ?int &$aboveBaseLevel = null, ?array &$directoryParts = null, ?string &$error = null): bool
    {
        if ($part === '..') {
            if (count($directoryParts) === 0) {
                if ($this->myIsAbsolute) {
                    $error = 'Absolute path is above root level.';

                    return false;
                }

                $aboveBaseLevel++;

                return true;
            }

            array_pop($directoryParts);

            return true;
        }

        $directoryParts[] = $part;

        return true;
    }