core-bundle/src/Resources/contao/dca/tl_style_sheet.php
public function scheduleUpdate($id)
	{
		// The onsubmit_callback passes a DataContainer object
		if (\is_object($id))
		{
			$id = $id->id;
		}

		// Return if there is no ID
		if (!$id || Contao\Input::get('act') == 'copy')
		{
			return;
		}

		/** @var Symfony\Component\HttpFoundation\Session\SessionInterface $objSession */
		$objSession = Contao\System::getContainer()->get('session');

		// Store the ID in the session
		$session = $objSession->get('style_sheet_updater');
		$session[] = $id;
		$objSession->set('style_sheet_updater', array_unique($session));
	}
public function scheduleUpdate($id)
	{
		// The onsubmit_callback passes a DataContainer object
		if (\is_object($id))
		{
			$id = $id->id;
		}

		// Return if there is no ID
		if (!$id || Contao\Input::get('act') == 'copy')
		{
			return;
		}

		/** @var Symfony\Component\HttpFoundation\Session\SessionInterface $objSession */
		$objSession = Contao\System::getContainer()->get('session');

		// Store the ID in the session
		$session = $objSession->get('style_sheet_updater');
		$session[] = $id;
		$objSession->set('style_sheet_updater', array_unique($session));
	}
Schedule a style sheet update

This method is triggered when a single style sheet or multiple style
sheets are modified (edit/editAll) or duplicated (copy/copyAll).

@param mixed $id