public function &addRowFooterColumns($columns = null, $properties = [])
    {
        $tableRow = $this->tFoot->addItem(new TrTag());
        if (is_array($columns)) {
            foreach ($columns as $column) {
                if (is_object($column) && method_exists($column, 'getTagType') && $column->getTagType()
                    == 'th') {
                    $tableRow->addItem($column);
                } else {
                    $tableRow->addItem(new ThTag($column, $properties));
                }
            }
        }

        return $tableRow;
    }