Emperors of the Holy Roman Empire (962–1806) were elected by a set circle of prince-electors. Among them were both secular electors as well as the archbishops of Mainz, Trier, and Cologne.
In principle promotion in the ranks of the Roman Catholic church was possible also for commoners also back then. E.g. clearly not all abbots or ordinary bishops where from the (high) nobility, although I assume most archbishops were.
So do we know if all the archbishops who served as (ecclesiastic) prince-electors during the centuries of the empire's existence belonged to noble families by birth (as would seem likely) or were there exceptions (as would seem possible on the face of it)?