code: def header_rows(self):
          
          # TO BE FIX: refactor
          header_rows = []
          headers = [col.header for col in self.columns]
          for header in headers:
              if len(header_rows) <= header.row_order:
                  header_rows.append([])
              header_rows[header.row_order].append(header)
          return header_rows
docs: [ [header1], [header3, header4] ]