Question - Default Sub-application
Answer -
To maintain backward compatibility, Struts 1.1 allows one default sub-application per application. The URI of the resources (i.e. JSPs, HTMLs, etc) in the default sub-application will have an empty sub-app prefix. This means when an existing 1.0 application is "dropped" into Struts 1.1, theoretically, it will automatically become the default sub-application.