code: function radioValue(group, items, itemId) {
      var targetItemId = itemId || group.checkedItem, value,
        CLASS_PREFIX_TYPE = CLASS_PREFIX_ICON + 'radio-';
      group.items.forEach(function(itemId) {
        var item = items[itemId], options = item.options, checked;
        if (itemId === targetItemId) {
          checked = true;
          group.checkedItem = itemId;
          value = item.value;
        } else {
          checked = false;
        }
        if (checked !== item.checked) {
          item.checked = options.checked = options.selected = checked;
          if (item.$elm) {
            item.$elm.removeClass(CLASS_PREFIX_TYPE + (checked ? 'off' : 'on'))
              .addClass(CLASS_PREFIX_TYPE + (checked ? 'on' : 'off'));
          }
        }
      });
      return value;
    }
docs: All instances 
  @param {group} group - Target `group`.
  @param {items} items - `items` to reference.
  @param {string} [itemId] - `itemId` of new checked item in this group.
  @returns {any} `value` of new or current checked item.