This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
handler.on("GetViewerPreferences", function (data) {
      return pdfManager.ensureCatalog("viewerPreferences");
    });
    handler.on("GetOpenAction", function (data) {
      return pdfManager.ensureCatalog("openAction");
    });
    handler.on("GetAttachments", function wphSetupGetAttachments(data) {
      return pdfManager.ensureCatalog("attachments");
    });
    handler.on("GetJavaScript", function wphSetupGetJavaScript(data) {
      return pdfManager.ensureCatalog("javaScript");
    });
    handler.on("GetDocJSActions", function wphSetupGetDocJSActions(data) {
      return pdfManager.ensureCatalog("jsActions");
    });
    handler.on("GetPageJSActions", function ({ pageIndex }) {
      return pdfManager.getPage(pageIndex).then(function (page) {
        return page.jsActions;
      });
    });
    handler.on("GetOutline", function wphSetupGetOutline(data) {
      return pdfManager.ensureCatalog("documentOutline");
    });
    handler.on("GetOptionalContentConfig", function (data) {
      return pdfManager.ensureCatalog("optionalContentConfig");
    });
    handler.on("GetPermissions", function (data) {
      return pdfManager.ensureCatalog("permissions");
    });
    handler.on("GetMetadata", function wphSetupGetMetadata(data) {