public function getFormat()
    {
        $result = null;

        foreach (static::$_formats as $value => $media_types)
        {
            $media_type = $this->getContentType();

            if (in_array($media_type, (array)$media_types))
            {
                $result = $value;
                break;
            }
        }

        return $result;
    }