invalid paths - how are they handled

[Bosko Vukojevic]

Two of our existing apps are built with different Struts versions:
    1.1 and 1.0
 
I am not able to find information on how Struts framework handles invalid paths 
or where to tweak the existing capability. 
 
If this is a valid path:
    /en/ca/home.do
what is going to be returned to the user in this case:
    www.ourApplication.com/app/en/ca/homeFFFFF.do
 
Some kind of existing HTTP error (404 or similar) or something else?
 
thanks ...