code: public RemoteWebDriverBuilder addAlternative(Capabilities options) {
      Map<String, Object> serialized = validate(Objects.requireNonNull(options));
      this.options.add(serialized);
      return this;
    }
docs: Add to the list of possible configurations that might be asked for. It is possible to ask for
  more than one type of browser per session. For example, perhaps you have an extension that is
  available for two different kinds of browser, and you'd like to test it).