code: function(isoString, pointSpan) {
              var i18n = Splunk.JSCharting.i18nUtils,
                  bdTime = this.extractBdTime(isoString),
                  dateObject;
  
              if(bdTime.isInvalid) {
                  return null;
              }
              dateObject = this.bdTimeToDateObject(bdTime);
  
              if (pointSpan >= this.MIN_SECS_PER_DAY) { // day or larger
                  return i18n.format_date(dateObject);
              }
              else if (pointSpan >= this.SECS_PER_MIN) { // minute or longer
                  return format_datetime(dateObject, 'medium', 'short');
              }
              return format_datetime(dateObject);
          }
docs: returns null if string cannot be parsed