The SmartPlant schema configuration file references the SmartPlant schema file (read-only), other schema files (read-only), and your schema extensions file (editable). The delivered schema extension file is named Extensions1.xml, and when you open EFSchema.cfg, your changes are saved in Extensions1.xml, by default. However, you can specify additional extension files to store your schema modifications. For more information, see SmartPlant Schema Editor Overview.