Prado\Web\UI\TPage::beginFormRender PHP Метод

    public function beginFormRender($writer)
    {
        if ($this->_formRendered) {
            throw new TConfigurationException('page_form_duplicated');
        }
        $this->_formRendered = true;
        $this->getClientScript()->registerHiddenField(self::FIELD_PAGESTATE, $this->getClientState());
        $this->_inFormRender = true;
    }