public function msginitFile(string $filename): PoFile
    {
        if (!is_readable($filename)) {
            $source = false;
        } else {
            $source = file_get_contents($filename);
        }
        if (false===$source) {
            throw new FileNotReadableException($filename);
        }
        return $this->msginitString($source, $filename);
    }