code: function(year) {
          year = this._validateYear(year);
  
          var monthDaysTable = LUNAR_MONTH_DAYS[year - LUNAR_MONTH_DAYS[0]];
          var intercalaryMonth = monthDaysTable >> 13;
  
          return intercalaryMonth;
      }
docs: Determine the intercalary month of a year (if any).
  @memberof ChineseCalendar
  @param year {CDate|number} The date to examine or the year to examine.
  @return {number} The intercalary month number, or 0 if none.
  @throws Error if an invalid year or a different calendar used.