A base configuration file named struts-default.xml is included in the struts2.jar file. This file is automatically included into struts.xml file to provide the standard configuration settings without having to copy them.
To exclude the struts-default.xml or to provide your own version, see the struts.configuration.files setting in struts.properties.
The contents of struts-default.xml are here:
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This file defines all of the default bundled results and interceptors and many interceptor stacks which you can use either as-is or as a basis for your own application-specific interceptor stacks. Notice the name of the package is "struts-default".