- Allow `m.fully_read` markers to be set from `/receipts`, as per [MSC2285](https://github.com/matrix-org/matrix-spec-proposals/pull/2285). ([#1216](https://github.com/matrix-org/matrix-spec/issues/1216))
- Add threading via `m.thread` relations, as per [MSC3440](https://github.com/matrix-org/matrix-spec-proposals/pull/3440), [MSC3816](https://github.com/matrix-org/matrix-spec-proposals/pull/3816), [MSC3856](https://github.com/matrix-org/matrix-spec-proposals/pull/3856), and [MSC3715](https://github.com/matrix-org/matrix-spec-proposals/pull/3715). ([#1254](https://github.com/matrix-org/matrix-spec/issues/1254))
- Add per-thread notifications and read receipts, as per [MSC3771](https://github.com/matrix-org/matrix-spec-proposals/pull/3771) and [MSC3773](https://github.com/matrix-org/matrix-spec-proposals/pull/3773). ([#1255](https://github.com/matrix-org/matrix-spec/issues/1255))
- Add `thread_id` to the `/receipt` endpoint, as per [MSC3771](https://github.com/matrix-org/matrix-spec-proposals/pull/3771). ([#1261](https://github.com/matrix-org/matrix-spec/issues/1261))
<strong>Spec Clarifications</strong>
- Mention that the `/rooms/{roomId}/invite` endpoint will return a 200 response if the user is already invited to the room. ([#1084](https://github.com/matrix-org/matrix-spec/issues/1084))
- Fix various typos throughout the specification. ([#1135](https://github.com/matrix-org/matrix-spec/issues/1135), [#1161](https://github.com/matrix-org/matrix-spec/issues/1161), [#1164](https://github.com/matrix-org/matrix-spec/issues/1164), [#1170](https://github.com/matrix-org/matrix-spec/issues/1170), [#1180](https://github.com/matrix-org/matrix-spec/issues/1180), [#1215](https://github.com/matrix-org/matrix-spec/issues/1215), [#1238](https://github.com/matrix-org/matrix-spec/issues/1238), [#1243](https://github.com/matrix-org/matrix-spec/issues/1243))
- Fix various typos throughout the specification. ([#1135](https://github.com/matrix-org/matrix-spec/issues/1135), [#1161](https://github.com/matrix-org/matrix-spec/issues/1161), [#1164](https://github.com/matrix-org/matrix-spec/issues/1164), [#1170](https://github.com/matrix-org/matrix-spec/issues/1170), [#1180](https://github.com/matrix-org/matrix-spec/issues/1180), [#1215](https://github.com/matrix-org/matrix-spec/issues/1215), [#1238](https://github.com/matrix-org/matrix-spec/issues/1238), [#1243](https://github.com/matrix-org/matrix-spec/issues/1243), [#1263](https://github.com/matrix-org/matrix-spec/issues/1263))
- Describe return codes for account data endpoints, and clarify that per-room data does not inherit from the global data. ([#1155](https://github.com/matrix-org/matrix-spec/issues/1155))
- Clarify that policy rule globs work like ACL globs. Contributed by Nico. ([#1165](https://github.com/matrix-org/matrix-spec/issues/1165))
- Clarify the format of some structures in the End-to-end encryption module. ([#1166](https://github.com/matrix-org/matrix-spec/issues/1166))