The start_call function, GoTo exception and fail page jumps normally jump to a page within their own project, but it is possible they could divert to a sub project.
Tests here explore such diversions, using the skis project, which is always available as a sub-project.
Test1 - the button below would normally link to a no-op responder which leads to the home page. But start_call directs this to skis,test1
Test2 - start_call diverts to bbc
Test3 - GoTo exception jumps to skis,test1
Test4 - inserts an error message into skis,server_error page. In this case the responder target is a page in a sub project.