Postman pre-request scripts seem to have both request and pm.request variables available. They seem to be different types. What's the difference between these / for what purposes should each be used?

The context is writing a pre-request script for Hawk authentication https://gist.github.com/michalc/b3f03e9234a2916810af12fa1d6c44af (to extend it a bit beyond Postman's built-in one / work around a suspected bug)