public function validate()
    {
        $result = parent::validate();

        //whitelist allowed URL schemes
        $allowed_schemes = array('http', 'https');
        if ($matches = parse_url($this->IFrameURL)) {
            if (isset($matches['scheme']) && !in_array($matches['scheme'], $allowed_schemes)) {
                $result->addError(_t(__CLASS__ . '.VALIDATION_BANNEDURLSCHEME', "This URL scheme is not allowed."));
            }
        }

        return $result;
    }