code: function(id) {
              if (controller.isResumable(id) && handler.pause && controller.isValid(id) && handler.pause(id)) {
                  connectionManager.free(id);
                  handler.moveInProgressToRemaining(id);
                  return true;
              }
              return false;
          }
docs: Attempts to pause the associated upload if the specific handler supports this and the file is "valid".
  @param id ID of the upload/file to pause
  @returns {boolean} true if the upload was paused