    public static function unichr($code) {
        if($code > 1114111 or $code < 0 or
          ($code >= 55296 and $code <= 57343) ) {
            // bits are set outside the "valid" range as defined
            // by UNICODE 4.1.0
            return '';
        }

        $x = $y = $z = $w = 0;
        if ($code < 128) {
            // regular ASCII character
            $x = $code;
        } else {
            // set up bits for UTF-8
            $x = ($code & 63) | 128;
            if ($code < 2048) {
                $y = (($code & 2047) >> 6) | 192;
            } else {
                $y = (($code & 4032) >> 6) | 128;
                if($code < 65536) {
                    $z = (($code >> 12) & 15) | 224;
                } else {
                    $z = (($code >> 12) & 63) | 128;
                    $w = (($code >> 18) & 7)  | 240;
                }
            }
        }
        // set up the actual character
        $ret = '';
        if($w) $ret .= chr($w);
        if($z) $ret .= chr($z);
        if($y) $ret .= chr($y);
        $ret .= chr($x);

        return $ret;
    }
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.