UIDs of anti-linked Personas.
No UIDs may be
null. Well-formed but non-existent UIDs (i.e. UIDs which can be successfully parsed, but which don't
currently correspond to a Persona instance) are permitted, as personas may appear
and disappear over time.
The special UID
* is used as a wildcard to mark the persona as globally anti-linked. See
It is expected, but not guaranteed, that anti-links made between personas will be reciprocal. That is, if persona A lists persona B's UID in its AntiLinkable.anti_links set, persona B will typically also list persona A in its anti-links set.