private DataType createReferenceType(int id, DocumentmanagerConfig.Datatype.Referencetype refType) {
            int targetId = refType.target_type_id();
            DocumentType targetDocType = (DocumentType) typesById.get(targetId);
            var type = new ReferenceDataType(targetDocType, id);
            inProgress(type);
            return type;
        }
One-shot configuration; should be called on a newly constructed manager
document/src/main/java/com/yahoo/document/DocumentTypeManagerConfigurer.java