private static function isHeader(array $entry): bool
    {
        $headerKeys = [
            'Project-Id-Version' => false,
            'PO-Revision-Date'   => false,
            'MIME-Version'       => false,
        ];

        $keys        = \array_keys($headerKeys);
        $headerItems = 0;
        $headers     = \array_map('trim', $entry['msgstr']);

        foreach ($headers as $header) {
            \preg_match_all('/(.*):\s/', $header, $matches, \PREG_SET_ORDER);

            if (isset($matches[0]) && \in_array($matches[0][1], $keys, true)) {
                $headerItems++;

                unset($headerKeys[$matches[0][1]]);

                $keys = \array_keys($headerKeys);
            }
        }

        return $headerItems !== 0;
    }