protected function split($string, $config, $context)
    {
        // OPTIMIZABLE!
        // do the preg_match, capture all subpatterns for reformulation

        // we don't support U+00A1 and up codepoints or
        // escaping because I don't know how to do that with regexps
        // and plus it would complicate optimization efforts (you never
        // see that anyway).
        $pattern = '/(?:(?<=\s)|\A)' . // look behind for space or string start
            '((?:--|-?[A-Za-z_])[A-Za-z_\-0-9]*)' .
            '(?:(?=\s)|\z)/'; // look ahead for space or string end
        preg_match_all($pattern, $string, $matches);
        return $matches[1];
    }