public function phpdocSummary()
    {
        $content = $this->phpdocContent();
        if (!$content) {
            return UNDEFINED;
        }
        $lines = preg_split('/(\n|\r\n)/', $content);
        $summary = '';
        foreach ($lines as $line) {
            $summary .= $line . "\n";
            if ($line === '' || substr($line, -1) === '.') {
                return trim($summary);
            }
        }
        $summary = trim($summary);
        if ($summary === '') {
            return UNDEFINED;
        }

        return $summary;
    }