code: public function renderColumnGroup()
      {
          foreach ($this->columns as $column) {
              /* @var $column Column */
              if (!empty($column->options)) {
                  $cols = [];
                  foreach ($this->columns as $col) {
                      $cols[] = Html::tag('col', '', $col->options);
                  }
  
                  return Html::tag('colgroup', implode("\n", $cols));
              }
          }
  
          return false;
      }
docs: Renders the column group HTML.
  @return bool|string the column group HTML or `false` if no column group should be rendered.