Roster file format and roster vs registered users

Hi

Two part question:

1) What is the current format of the roster file in 17.04? I know that around 15.xx it seems to have gone to this:

[{<<"admin">>,<<"localhost">>,<<"Friend">>,<<"Admin">>},{<<"vipul">>,<<"localhost">>,<<"Friend">>,<<"Vipul">>}].

(from http://www.techiekunal.in/2016/04/ejabberd-bulk-roster-addition-using-pu...)

2) Is the difference between a roster and a registered user simply that the former is a list while the latter is also a registered account within mnesia/db backend?

Thanks,