public function format(Geo $geo)
    {
        return '<span class="h-geo">'
            . '<span class="p-latitude">' . (string)$geo->getLatitude() . '</span>, '
            . '<span class="p-longitude">' . (string)$geo->getLongitude() . '</span>'
            . ($geo->getAltitude() === null ? '' : ' (elevation <span class="p-altitude">' . (string)$geo->getAltitude() . '</span>)')
            . '</span>';
    }