The set of Personas encapsulated by this Individual.
There must always be at least one Persona in this set.
No order is specified over the set of personas, as such an order may be different across each of the properties implemented by the personas (e.g. should they be ordered by presence, name, star sign, etc.?).
Changing the set of personas may cause updates to the aggregated properties provided by the Individual, resulting in property notifications for them.
Changing the set of personas will not cause permanent linking/unlinking of the added/removed personas to/from this Individual. To do that, call IndividualAggregator.link_personas or IndividualAggregator.unlink_individual, which will ensure the link changes are written to the appropriate backend.