code: public function renderFilters()
      {
          if ($this->filterModel !== null) {
              $cells = [];
              foreach ($this->columns as $column) {
                  /* @var $column Column */
                  $cells[] = $column->renderFilterCell();
              }
  
              return Html::tag('tr', implode('', $cells), $this->filterRowOptions);
          }
  
          return '';
      }
docs: Renders the filter.
  @return string the rendering result.