code: function getEpoch(epoch) {
          if (!epoch) { return 0; }
          if (typeof epoch.getTime === "function") { return epoch.getTime(); }
          if (typeof epoch === "number") { return epoch; }
          throw new TypeError("now should be milliseconds since UNIX epoch");
      }
docs: Used to grok the `now` parameter to createClock.
  @param epoch {Date|number} the system time