boolean isPositionStruct(DocumentmanagerConfig.Doctype.Structtype cfg) {
                if (! cfg.name().equals(PositionDataType.STRUCT_NAME)) return false;
                if (! cfg.inherits().isEmpty()) return false;
                if (cfg.field().size() != 2) return false;
                var f0 = cfg.field(0);
                var f1 = cfg.field(1);
                if (! f0.name().equals(POS_X.getName())) return false;
                if (! f1.name().equals(POS_Y.getName())) return false;
                if (f0.internalid() != POS_X.getId()) return false;
                if (f1.internalid() != POS_Y.getId()) return false;
                if (typesByIdx.get(f0.type()) != POS_X.getDataType()) return false;
                if (typesByIdx.get(f1.type()) != POS_Y.getDataType()) return false;
                return true;
            }
One-shot configuration; should be called on a newly constructed manager
document/src/main/java/com/yahoo/document/DocumentTypeManagerConfigurer.java