code: private void buildOperationRef(MarkupDocBuilder markupDocBuilder, PathOperation operation) {
          buildOperationTitle(markupDocBuilder, crossReference(markupDocBuilder, operationDocumentResolverDefault.apply(operation), operation.getId(), operation.getTitle()), "ref-" + operation.getId());
      }
docs: Builds a cross-reference to a separated operation file
  
  @param markupDocBuilder the markupDocBuilder do use for output
  @param operation        the Swagger Operation