core-bundle/src/Resources/contao/forms/Form.php
protected function initializeSession($formId)
	{
		if (Input::post('FORM_SUBMIT') != $formId)
		{
			return;
		}

		$arrMessageBox = array('TL_ERROR', 'TL_CONFIRM', 'TL_INFO');
		$_SESSION['FORM_DATA'] = \is_array($_SESSION['FORM_DATA']) ? $_SESSION['FORM_DATA'] : array();

		foreach ($arrMessageBox as $tl)
		{
			if (\is_array($_SESSION[$formId][$tl]))
			{
				$_SESSION[$formId][$tl] = array_unique($_SESSION[$formId][$tl]);

				foreach ($_SESSION[$formId][$tl] as $message)
				{
					$objTemplate = new FrontendTemplate('form_message');
					$objTemplate->message = $message;
					$objTemplate->class = strtolower($tl);

					$this->Template->fields .= $objTemplate->parse() . "\n";
				}

				$_SESSION[$formId][$tl] = array();
			}
		}
	}
protected function initializeSession($formId)
	{
		if (Input::post('FORM_SUBMIT') != $formId)
		{
			return;
		}

		$arrMessageBox = array('TL_ERROR', 'TL_CONFIRM', 'TL_INFO');
		$_SESSION['FORM_DATA'] = \is_array($_SESSION['FORM_DATA']) ? $_SESSION['FORM_DATA'] : array();

		foreach ($arrMessageBox as $tl)
		{
			if (\is_array($_SESSION[$formId][$tl]))
			{
				$_SESSION[$formId][$tl] = array_unique($_SESSION[$formId][$tl]);

				foreach ($_SESSION[$formId][$tl] as $message)
				{
					$objTemplate = new FrontendTemplate('form_message');
					$objTemplate->message = $message;
					$objTemplate->class = strtolower($tl);

					$this->Template->fields .= $objTemplate->parse() . "\n";
				}

				$_SESSION[$formId][$tl] = array();
			}
		}
	}
Initialize the form in the current session

@param string $formId