parentThreadId property
The threadId of the exchange containing this one, where this exchange is
conducted inside another (§4.9.2).
A navigation aid. It records one level of containment and does not
change which exchange attests an event — §4.9.1 governs that, and holds
whether or not this member is present. Like threadId it carries no
normative validation semantics: a consumer MUST NOT reject a document on
the basis of parentThreadId alone.
Implementation
final String? parentThreadId;