Stefano Segantin

Something like this? ```Python @property def domains(self): return self._domains @domains.setter def domains(self, d): if not isinstance(d, MutableSequence): d = [d] allowed_domain_types = (openmc.Cell, openmc.Material, openmc.Universe) cv.check_iterable_type('source domains', d, allowed_domain_types) self._domains...

That is already in the latest commit. I am not very familiar with how to use `checkvalue`. Do you suggest to use `cv.CheckedList` in here: ```python def domains(self, d): if...

yes, I have. it does that for all the models I have, actually.