actionpack-3.0.3/lib/action_dispatch/middleware/rescue.rb

I was trying to understand how exceptions are caught. There are two
rescue.rb files. One is under ActionController. I understand how it is
invoked and what it does. But the one under action_dispatch I don't see
how it gets used.

I see the autoload for it in actionpack-3.0.3/lib/action_dispatch.rb but
I don't see a Rescue class created anywhere.

Can someone help me to understand this part of the code?

Thank you in advance.

Perry