protected function _fontFamilyCB($m)
    {
        // Issue 210: must not eliminate WS between words in unquoted families
        $flags = PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY;
        $pieces = preg_split('/(\'[^\']+\'|"[^"]+")/', $m[1], null, $flags);
        $out = 'font-family:';

        while (null !== ($piece = array_shift($pieces))) {
            if ($piece[0] !== '"' && $piece[0] !== "'") {
                $piece = preg_replace('/\\s+/', ' ', $piece);
                $piece = preg_replace('/\\s?,\\s?/', ',', $piece);
            }
            $out .= $piece;
        }

        return $out . $m[2];
    }