BpmnMigrationMapping : An operator’s assertion about how a source version’s elements correspond to a target version’s (#925). Elements not named here are implicitly mapped to their own id – and are then subject to every rule an explicit mapping is. 1:1 only: 1:N is deliberately not representable (it would require the engine to synthesize tokens, and inside an inclusive region the JoinState that inclusive_join never creates), and N:1 is representable only so that it can be refused with a reason.