Contao\SelectMenu::__set PHP Method

    public function __set($strKey, $varValue)
    {
        switch ($strKey) {
            case 'mandatory':
                if ($varValue) {
                    $this->arrAttributes['required'] = 'required';
                } else {
                    unset($this->arrAttributes['required']);
                }
                parent::__set($strKey, $varValue);
                break;
            case 'size':
                if ($this->multiple) {
                    $this->arrAttributes['size'] = $varValue;
                }
                break;
            case 'multiple':
                if ($varValue) {
                    $this->arrAttributes['multiple'] = 'multiple';
                }
                break;
            case 'options':
                $this->arrOptions = \StringUtil::deserialize($varValue);
                break;
            default:
                parent::__set($strKey, $varValue);
                break;
        }
    }