clarification of AuthnRequest protocol

In section 3.4.1.4 of Core, it says "The resulting assertion(s) MUST
contain a <saml:AudienceRestriction> element referencing the requester
as an acceptable relying party."  What if the requester is in fact the
requested subject, but beyond that the relying party is unspecified?
What should the Audience value be in that case?

Thanks,
Tom