code: function Worker(opt) {
      // Create the root parent for the proto chain, and the starting Worker.
      var root = Object.assign(Worker.convert(Promise.resolve()),
        JSON.parse(JSON.stringify(Worker.template)));
      var self = Worker.convert(Promise.resolve(), root);
  
      // Set progress, optional settings, and return.
      self = self.setProgress(1, Worker, 1, [Worker]);
      self = self.set(opt);
      return self;
    }
docs: /* ----- CONSTRUCTOR -----