yii\grid\GridView::renderFilters PHP Method

    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);
        } else {
            return '';
        }
    }