docs: def check(self):
          """Check this transaction for completeness"""
          if not self.date:
              raise XnDataError("Missing date")
          if not self.desc:
              raise XnDataError("Missing description")
          if not self.dst:
              raise XnDataError("No destination accounts")
          if not self.src:
              raise XnDataError("No source accounts")
          if not self.amount:
              raise XnDataError("No transaction amount")