Validate the list that represents the table header.

        :param hed: The list that represents the table header.
        :type hed: list(list(hatemile.util.html.htmldomelement.HTMLDOMElement))
        :return: True if the table header is valid or False if the table header
                 is not valid.
        :rtype: bool

def _validate_header(self, hed):
        """
        Validate the list that represents the table header.

        :param hed: The list that represents the table header.
        :type hed: list(list(hatemile.util.html.htmldomelement.HTMLDOMElement))
        :return: True if the table header is valid or False if the table header
                 is not valid.
        :rtype: bool
        """
        # pylint: disable=no-self-use

        if not bool(hed):
            return False
        length = -1
        for row in hed:
            if not bool(row):
                return False
            elif length == -1:
                length = len(row)
            elif len(row) != length:
                return False
        return True