code: function() {
          var $ths = this.$el.find('th');
          var columnNames, mergedColumnNames;
  
          if (this.selectionModel.hasSelection()) {
              columnNames = this._getSelectedColumnNames();
          } else if (this.focusModel.has(true)) {
              columnNames = [this.focusModel.get('columnName')];
          }
  
          $ths.removeClass(classNameConst.CELL_SELECTED);
          if (columnNames) {
              mergedColumnNames = this._getContainingMergedColumnNames(columnNames);
              _.each(columnNames.concat(mergedColumnNames), function(columnName) {
                  $ths.filter('[' + ATTR_COLUMN_NAME + '="' + columnName + '"]').addClass(classNameConst.CELL_SELECTED);
              });
          }
      }
docs: Refreshes selected class of every header element (th)
  @private