    public function toString() {
        // reconstruct authority
        $authority = null;
        // there is a rendering difference between a null authority
        // (http:foo-bar) and an empty string authority
        // (http:///foo-bar).
        if (!is_null($this->host)) {
            $authority = '';
            if(!is_null($this->userinfo)) $authority .= $this->userinfo . '@';
            $authority .= $this->host;
            if(!is_null($this->port))     $authority .= ':' . $this->port;
        }

        // Reconstruct the result
        // One might wonder about parsing quirks from browsers after
        // this reconstruction.  Unfortunately, parsing behavior depends
        // on what *scheme* was employed (file:///foo is handled *very*
        // differently than http:///foo), so unfortunately we have to
        // defer to the schemes to do the right thing.
        $result = '';
        if (!is_null($this->scheme))    $result .= $this->scheme . ':';
        if (!is_null($authority))       $result .=  '//' . $authority;
        $result .= $this->path;
        if (!is_null($this->query))     $result .= '?' . $this->query;
        if (!is_null($this->fragment))  $result .= '#' . $this->fragment;

        return $result;
    }
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.