Manual:DefaultSettings.php/en

DefaultSettings.php contains default configuration settings.

As of MediaWiki 1.38, including  in your   will result in the error described at T311966:

PHP Fatal error: Uncaught FatalError: $wgBaseDirectory must not be modified in settings files! Use the MW_INSTALL_PATH environment variable to override the installation root directory. in /var/www/html/w/includes/Setup.php:237 Stack trace: thrown in /var/www/html/w/includes/Setup.php on line 237
 * 1) 0 /var/www/html/w/maintenance/doMaintenance.php(96): require_once
 * 2) 1 /var/www/html/w/maintenance/update.php(264): require_once('/var/www/html/w...')
 * 3) 2 {main}

Fatal error: Uncaught FatalError: $wgBaseDirectory must not be modified in settings files! Use the MW_INSTALL_PATH environment variable to override the installation root directory. in /var/www/html/w/includes/Setup.php:237 Stack trace: thrown in /var/www/html/w/includes/Setup.php on line 237
 * 1) 0 /var/www/html/w/maintenance/doMaintenance.php(96): require_once
 * 2) 1 /var/www/html/w/maintenance/update.php(264): require_once('/var/www/html/w...')
 * 3) 2 {main}