protected function SetRequired($name, $errorPrefix = '')
    {
        $field = $this->GetElement($name);
        if (!$field instanceof FormField)
        {
            throw new \InvalidArgumentException("$name is not a field in the form elements");
        }
        if (!$errorPrefix)
        {
            $errorPrefix = $this->ErrorPrefix($name);
        }
        $field->SetRequired($errorPrefix);
    }