code: protected function renderDataCellContent($model, $key, $index)
      {
          if ($this->content !== null) {
              return parent::renderDataCellContent($model, $key, $index);
          }
  
          if ($this->checkboxOptions instanceof Closure) {
              $options = call_user_func($this->checkboxOptions, $model, $key, $index, $this);
          } else {
              $options = $this->checkboxOptions;
          }
  
          if (!isset($options['value'])) {
              $options['value'] = is_array($key) ? Json::encode($key) : $key;
          }
  
          if ($this->cssClass !== null) {
              Html::addCssClass($options, $this->cssClass);
          }
  
          return Html::checkbox($this->name, !empty($options['checked']), $options);
      }
docs: {@inheritdoc}