docs: def _iterate_fields_cond(self, pkt, val, use_val):
          """Internal function used by _find_fld_pkt & _find_fld_pkt_val"""
          # Iterate through the fields
          for fld, cond in self.flds:
              if isinstance(cond, tuple):
                  if use_val:
                      if cond[1](pkt, val):
                          return fld
                      continue
                  else:
                      cond = cond[0]
              if cond(pkt):
                  return fld
          return self.dflt