code: function(id) {
              var itemLimit = this._currentItemLimit,
                  fileName;
  
              if (this._preventRetries[id]) {
                  this.log("Retries are forbidden for id " + id, "warn");
                  return false;
              }
              else if (this._handler.isValid(id)) {
                  fileName = this.getName(id);
  
                  if (this._options.callbacks.onManualRetry(id, fileName) === false) {
                      return false;
                  }
  
                  if (itemLimit > 0 && this._netUploadedOrQueued + 1 > itemLimit) {
                      this._itemError("retryFailTooManyItems");
                      return false;
                  }
  
                  this.log("Retrying upload for '" + fileName + "' (id: " + id + ")...");
                  return true;
              }
              else {
                  this.log("'" + id + "' is not a valid file ID", "error");
                  return false;
              }
          }
docs: return false if we should not attempt the requested retry