code: function Calendar(firstweekday) {
        this._firstweekday = typeof(firstweekday) === "undefined" ? 0 : firstweekday;
  
        if(firstweekday < 0 || firstweekday > 6) {
          throw new IllegalWeekdayError();
        }
  
        this._oneday = 1000 * 60 * 60 * 24;
        this._onehour = 1000 * 60 * 60;
      }
docs: Base calendar class. This class doesn't do any formatting. It simply
  provides data to subclasses.
  
  @param {Number} firstweekday
  @throws {IllegalWeekdayError} If the provided firstweekday is invalid.
  @api public