[exim] Using "or" in ACL condition statement

I want to write an ACL condition that will accept mail if one of three
conditions is true. I can create the actual conditions, but I'm having
problems with the syntax of the "or" operator. To test this, I have an ACL
as follows:

accept  domains       = +relay_to_domains
        endpass
        message       = Unknown user
        condition     = or{{0}{1}}

That gives an error: invalid "condition" value "or{{0}{1}}"

So I tried replacing the condition with "${if eq {or{{0}{1}}}{1}}", which
gives: invalid "condition" value "}{1}}"

Can someone point me in the right direction here, please?

Thanks,
Keith