code: function(jd) {
  			jd -= this.jdEpoch;
  			var day = mod(jd + 8 + ((18 - 1) * 20), 365);
  			return [Math.floor(day / 20) + 1, mod(day, 20)];
  		}
docs: Retrieve Haab date from a Julian date.
  @memberof MayanCalendar
  @private
  @param jd  {number} The Julian date.
  @return {number[]} Corresponding Haab month and day.