Problem understanding Messaging Templates when used with Notifications

I am trying to set up Notifications to work on my site.

I think I have at last mastered the Messaging Templates (different module I know) but I don't understand the relationship between what Messaging refers to as Digests and the Notifications setting for Intervals. In Notifications Settings I can choose between None, Short or Long for Digest Method. Which Messaging Template does each one of these settings invoke? Putting that question the other way round, which Messaging Template do I re-write to change what appears for Short and Long Digest methods?