public static function xpathLiteral($s)
    {
        if (false === strpos($s, "'")) {
            return sprintf("'%s'", $s);
        }

        if (false === strpos($s, '"')) {
            return sprintf('"%s"', $s);
        }

        $string = $s;
        $parts = [];
        while (true) {
            if (false !== $pos = strpos($string, "'")) {
                $parts[] = sprintf("'%s'", substr($string, 0, $pos));
                $parts[] = "\"'\"";
                $string = substr($string, $pos + 1);
            } else {
                $parts[] = "'$string'";
                break;
            }
        }

        return sprintf('concat(%s)', implode(', ', $parts));
    }