Set the scope of header cells of table header.

        :param table_header: The table header.
        :type table_header: hatemile.util.html.htmldomelement.HTMLDOMElement

def _prepare_header_cells(self, table_header):
        """
        Set the scope of header cells of table header.

        :param table_header: The table header.
        :type table_header: hatemile.util.html.htmldomelement.HTMLDOMElement
        """

        cells = self.parser.find(table_header).find_children(
            'tr'
        ).find_children('th').list_results()
        for cell in cells:
            self.id_generator.generate_id(cell)

            cell.set_attribute('scope', 'col')