private function getTableHf()
    {
        if ($this->HFContent) return $this->HFContent;

        ob_start();
        ?>
        <tr>
            <?php // Start constructing the table header columns ?>
            <?php foreach ($this->columns as $column_key => $column_options) : ?>

                <?php $sortable_class = $this->getSortableClass($column_key); ?>

                <th data-column-name="<?php echo $column_key; ?>"
                    class="<?php echo $sortable_class; ?> <?php echo $this->getColumnOption($column_key, self::COLUMN_OPTION_CLASSES); ?>"
                    <?php echo $this->getColumnOption($column_key, self::COLUMN_OPTION_THEAD_ATTR) ?>>

                    <?php echo $this->getColumnHeaderStructure($column_key, $column_options); ?>
                </th>
            <?php endforeach; ?>
        </tr>

        <?php

        $this->HFContent = ob_get_clean();

        return $this->HFContent;
    }