code: function isYearSeparator() {
      if (yearSeparator !== null) {
        return yearSeparator;
      }
  
      var formatter = makeFormatter({day: 'numeric', month: 'short', year: 'numeric'});
      if (formatter) {
        var output = formatter.format(new Date(0));
        yearSeparator = !!output.match(/\d,/);
        return yearSeparator;
      } else {
        return true;
      }
    }
docs: Private: Determine if the year should be separated from the month and day with a comma. For example, `9 Jun 2014` in en-GB and `Jun 9, 2014` in en-US.  Returns true if the date needs a separator.