docs: def validate(self, ticket=None, raise_=False):
          """
          Validates this receipt.
  
          This is a shortcut to :class:`~.ReceiptQuerySet`'s method of the same
          name. Calling this validates only this instance.
  
          :param AuthTicket ticket: Use this ticket. If None, one will be loaded
              or created automatically.
          :param bool raise_: If True, an exception will be raised when
              validation fails.
          """
          # XXX: Maybe actually have this sortcut raise an exception?
          rv = Receipt.objects.filter(pk=self.pk).validate(ticket)
          # Since we're operating via a queryset, this instance isn't properly
          # updated:
          self.refresh_from_db()
          if raise_ and rv:
              raise exceptions.ValidationError(rv[0])
          return rv