code: function(d) {
      if (d.wyExtent) return d.wyExtent;
  
      // go to start of ISO week to get to the right year
      var year = later.dw.next(later.wy.start(d), 5),
          dwFirst = later.dw.val(later.Y.start(year)),
          dwLast = later.dw.val(later.Y.end(year));
  
      return (d.wyExtent = [1, dwFirst === 5 || dwLast === 5 ? 53 : 52]);
    }
docs: The minimum and maximum valid ISO week values for the year indicated.
  
  @param {Date} d: The date indicating the year to find ISO values for