code: public final PCB aCase(Consumer<CaseBuilder<P, PC>> caseBuilderConsumer) {
          Null.nonNullArg(caseBuilderConsumer, "caseBuilderConsumer");
          caseBuilderConsumer.accept(new CaseBuilder<>(this::partialCaseFactoryMethod));
          return self();
      }
docs: Builds full new case by lambda expression (presumably).