http://wiki.opensymphony.com/display/WW/Action+configuration
Since Webwork 2.2.1 you are also able to specify a default action to be executed when no other action is matched in the xwork.xml. This feature is provided mainly to eliminate the need to create an action class and/or element for very simple or similar results. The default action name can be set inside the package element like below:
<default-action-ref name="simpleViewResultAction">
This feature should be configured such that there is only one default action per namespace. Therefore if you have multiple packages declaring a default action with the same namespace, it is not guaranteed which action will be the default.