core-bundle/src/Resources/contao/library/Contao/Config.php
public static function preload()
	{
		// Load the default files
		include __DIR__ . '/../../config/default.php';
		include __DIR__ . '/../../config/agents.php';
		include __DIR__ . '/../../config/mimetypes.php';

		$rootDir = System::getContainer()->getParameter('kernel.project_dir');

		// Include the local configuration file
		if (($blnHasLcf = file_exists($rootDir . '/system/config/localconfig.php')) === true)
		{
			include $rootDir . '/system/config/localconfig.php';
		}

		static::loadParameters();

		static::$blnHasLcf = $blnHasLcf;
	}
public static function preload()
	{
		// Load the default files
		include __DIR__ . '/../../config/default.php';
		include __DIR__ . '/../../config/agents.php';
		include __DIR__ . '/../../config/mimetypes.php';

		$rootDir = System::getContainer()->getParameter('kernel.project_dir');

		// Include the local configuration file
		if (($blnHasLcf = file_exists($rootDir . '/system/config/localconfig.php')) === true)
		{
			include $rootDir . '/system/config/localconfig.php';
		}

		static::loadParameters();

		static::$blnHasLcf = $blnHasLcf;
	}
Preload the default and local configuration