code: function(year, month, day) {
          var date = this._validate(year, month, day, main.local.invalidMonth);
          var year = date.year();
          if (year < 0) { year++; } // No year zero
          var doy = date.day();
          for (var m = 1; m < date.month(); m++) {
              doy += this.daysPerMonth[m - 1];
          }
          return doy + gregorian.toJD(year + 1468, 3, 13);
      }
docs: Retrieve the Julian date equivalent for this date,
  i.e. days since January 1, 4713 BCE Greenwich noon.
  @memberof NanakshahiCalendar
  @param year {CDate|number} The date to convert or the year to convert.
  @param [month] {number} The month to convert.
  @param [day] {number} The day to convert.
  @return {number} The equivalent Julian date.
  @throws Error if an invalid date or a different calendar used.