[Dovecot] using OR in doveadm search query

Hi,

I am trying to create an OR query but no success yet:

$ doveadm search mailbox shared/* OR SUBJECT "a" SUBJECT "b" doveadm(neil): Fatal: Use parenthesis when mixing ANDs and ORs

$ doveadm search mailbox shared/* OR \(SUBJECT "a"\) \(SUBJECT "b"\) doveadm(neil): Fatal: Unknown argument (SUBJECT

$ doveadm search mailbox shared/* \(OR \(SUBJECT "a"\) \(SUBJECT "b"\)\) doveadm(neil): Fatal: Unknown argument (OR

What is the correct syntax for such a query?

-- Willem-Jan de Hoog