code: def get_min_row_num(mention):
      
      span = _to_span(mention)
      if span.sentence.is_tabular():
          return span.sentence.cell.row_start
      else:
          return None
docs: Return the lowest row number that a Mention occupies.
  
      :param mention: The Mention to evaluate. If a candidate is given, default
          to its first Mention.
      :rtype: integer or None