docs: def iterstruct(self):
          """Yield data structures built from the JSON header specifications in a table"""
          from rowgenerators.rowpipe.json import add_to_struct
  
          json_headers = self.json_headers
  
          for row in islice(self, 1, None): # islice skips header
              d = {}
              for pos, jh in json_headers:
                  add_to_struct(d, jh, row[pos])
              yield d