docs: def _find_fld_pkt_val(self, pkt, val):
          """Given a Packet instance `pkt` and the value `val` to be set,
  returns the Field subclass to be used, and the updated `val` if necessary.
  
          """
          fld = self._iterate_fields_cond(pkt, val, True)
          # Default ? (in this case, let's make sure it's up-do-date)
          dflts_pkt = pkt.default_fields
          if val == dflts_pkt[self.name] and self.name not in pkt.fields:
              dflts_pkt[self.name] = fld.default
              val = fld.default
          return fld, val