How to make choice between resources of internal and external modules?

Hi All

I want to use fallback functionality for my javascripts, css and other
resources. What I want to do is to use my internal modules css if available,
global modules(with the same name) css otherwise.
I am trying to get it through fallback but not able to get it.

I am not sure whether I am doing it in right way. Am I doing something wrong
here?

Thanks in advance.

-- 
Regards
Sac