[Dovecot] multiple authentication mechanisms/passwords for same account

This may be trivial but reading the documentation I can't find a clear answer:

If multiple authentication mechanisms (or multiple databases for one) are defined, does it allow one user account to have several (at least two) alternative passwords (so that any of them would work)?

Or does it first map an account to a fixed authentication mechanism/password and if it fails, others won't be tried?

-- Tapani Tarvainen