This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
{
              msgHandler: handler,
              password: source.password,
              length: fullRequest.contentLength,
              disableAutoFetch,
              rangeChunkSize: source.rangeChunkSize,
            },
            evaluatorOptions,
            docBaseUrl
          );
          
          
          
          for (let i = 0; i < cachedChunks.length; i++) {
            newPdfManager.sendProgressiveData(cachedChunks[i]);
          }
          cachedChunks = [];
          pdfManagerCapability.resolve(newPdfManager);
          cancelXHRs = null;
        })
        .catch(function (reason) {
          pdfManagerCapability.reject(reason);
          cancelXHRs = null;
        });
      var loaded = 0;
      var flushChunks = function () {
        var pdfFile = arraysToBytes(cachedChunks);
        if (source.length && pdfFile.length !== source.length) {
          warn("reported HTTP length is different from actual");
        }