thread property
Thread is whether a reply can be threaded UNDER a specific message. True for slack alone: it is the only transport whose ingress reports a thread (thread_ts, published as the envelope's replyTo) and whose send posts back into it. Discord's replyTo makes an inline reply rather than a thread, Telegram's and WhatsApp's each quote one message, and Teams carries no reply target at all — a replyTo sent to it is ignored.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
bool? thread;