This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
pdfManager.ensure(page, "view"),
        ]).then(function ([rotate, ref, userUnit, view]) {
          return {
            rotate,
            ref,
            userUnit,
            view,
          };
        });
      });
    });
    handler.on("GetPageIndex", function wphSetupGetPageIndex({ ref }) {
      const pageRef = Ref.get(ref.num, ref.gen);
      return pdfManager.ensureCatalog("getPageIndex", [pageRef]);
    });
    handler.on("GetDestinations", function wphSetupGetDestinations(data) {
      return pdfManager.ensureCatalog("destinations");
    });
    handler.on("GetDestination", function wphSetupGetDestination(data) {
      return pdfManager.ensureCatalog("getDestination", [data.id]);
    });
    handler.on("GetPageLabels", function wphSetupGetPageLabels(data) {
      return pdfManager.ensureCatalog("pageLabels");
    });
    handler.on("GetPageLayout", function wphSetupGetPageLayout(data) {
      return pdfManager.ensureCatalog("pageLayout");
    });
    handler.on("GetPageMode", function wphSetupGetPageMode(data) {
      return pdfManager.ensureCatalog("pageMode");
    });