Oxygen XML Editor stores the master files in a folder located in the Project view, as the first child of the project root. The Master Files Support is disabled by default. To enable the Master Files Support, go to the Settings menu of the Project view and select Enable Master Files Support. You can also select Enable Master Files Support from the contextual menu of the Master Files directory, or from the contextual menu of the project itself. Oxygen XML Editor allows you to enable/disable the Master Files Support for each project you are working on.