private function generateDocumentProperties(array $metadata)
    {
        $lines = [];

        foreach ($metadata['properties'] as $property) {
            $lines[] = $this->generatePropertyDocBlock($property);
            $lines[] = $this->spaces . $property['visibility'] . ' $' . $property['field_name'] . ";\n";
        }

        return implode("\n", $lines);
    }