docs: 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