def _new_or_old_field_property(prop, new_field, old_field, old_priority):
		"""
		Get the given property on the old field or the new field, with priority given
		to a field of the user's choosing.

		Arguments:
		prop -- a string of the requested property name
		old_field -- the old field as a Field instance
		new_field -- the new field as a Field instance
		old_priority -- a boolean that, if True, gives priority to the old
		                field, and, if False, gives priority to the new field

		Returns: the requested property on the new field or old field

		"""
		new_prop = getattr(new_field, prop)
		old_prop = getattr(old_field, prop)
		if old_priority:
			return old_prop or new_prop
		else:
			return new_prop or old_prop