<!-- Intentionally blank line to ensure headers work in the concatenated changelog -->
### Client-Server API
<strong>Deprecations</strong>
- Deprecate the `sender_key` and `device_id` on `m.megolm.v1.aes-sha2` events, and the `sender_key` on `m.room_key_request` to-device messages, as per [MSC3700](https://github.com/matrix-org/matrix-spec-proposals/pull/3700). ([#1101](https://github.com/matrix-org/matrix-spec/issues/1101))
<strong>Backwards Compatible Changes</strong>
- Make `from` optional on `GET /_matrix/client/v3/messages` to allow requesting events from the start or end of the room history, as per [MSC3567](https://github.com/matrix-org/matrix-spec-proposals/pull/3567). ([#1002](https://github.com/matrix-org/matrix-spec/issues/1002))
- Add refresh tokens, per [MSC2918](https://github.com/matrix-org/matrix-spec-proposals/pull/2918). ([#1056](https://github.com/matrix-org/matrix-spec/issues/1056), [#1113](https://github.com/matrix-org/matrix-spec/issues/1113))
- Relax the restrictions on Rich Replies, as per [MSC3676](https://github.com/matrix-org/matrix-spec-proposals/pull/3676). ([#1062](https://github.com/matrix-org/matrix-spec/issues/1062))
- Describe a structured system for event relationships, as per [MSC2674](https://github.com/matrix-org/matrix-spec-proposals/pull/2674). ([#1062](https://github.com/matrix-org/matrix-spec/issues/1062))
- Describe how relationships between events can be "aggregated", as per [MSC2675](https://github.com/matrix-org/matrix-spec-proposals/pull/2675) and [MSC3666](https://github.com/matrix-org/matrix-spec-proposals/pull/3666). ([#1062](https://github.com/matrix-org/matrix-spec/issues/1062))
- Add support for a new `knock_restricted` join rule in supported room versions, as per [MSC3787](https://github.com/matrix-org/matrix-spec-proposals/pull/3787). ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
<strong>Spec Clarifications</strong>
- Clarify that the url field in `m.room.avatar` events is not required. ([#987](https://github.com/matrix-org/matrix-spec/issues/987))
- Clarify that the `type` in user-interactive authentication can be omitted. ([#989](https://github.com/matrix-org/matrix-spec/issues/989))
- Adjust the OpenAPI specification so that the type `Flow information` is explicitly defined when the client-server API is rendered. ([#1003](https://github.com/matrix-org/matrix-spec/issues/1003))
- Correct the default value for `invite` where it is not specified in an `m.room.power_levels` event. ([#1021](https://github.com/matrix-org/matrix-spec/issues/1021))
- Update various links which pointed to the old `matrix-doc` github repository. ([#1032](https://github.com/matrix-org/matrix-spec/issues/1032))
- Removed `m.room.message.feedback` per [MSC3582](https://github.com/matrix-org/matrix-spec-proposals/pull/3582). ([#1035](https://github.com/matrix-org/matrix-spec/issues/1035))
- Clarify that state keys starting with `@` are in fact reserved. Regressed from [#3658](https://github.com/matrix-org/matrix-spec-proposals/pull/3658). ([#1100](https://github.com/matrix-org/matrix-spec/issues/1100))
- Remove unenforced size limit on the `name` field of `m.room.name` events. ([#3669](https://github.com/matrix-org/matrix-spec-proposals/issues/3669))
- Remove erroneous `room_id` field from examples of `m.read`, `m.typing` in `/sync` and `m.fully_read` in room account data. ([#3679](https://github.com/matrix-org/matrix-spec-proposals/issues/3679))
- Clarify the behaviour of `event_match` in push rule conditions. ([#3690](https://github.com/matrix-org/matrix-spec-proposals/issues/3690))
- Fix membership state transitions to denote that `invite->knock` and `external->leave` are valid transitions. ([#3730](https://github.com/matrix-org/matrix-spec-proposals/issues/3730))
- Add a `destination` property to the Authorization header, as per [MSC3383](https://github.com/matrix-org/matrix-spec-proposals/pull/3383). ([#1067](https://github.com/matrix-org/matrix-spec/issues/1067))
<strong>Spec Clarifications</strong>
- Remove largely unused `origin` field from PDUs. ([#998](https://github.com/matrix-org/matrix-spec/issues/998))
- Update various links which pointed to the old `matrix-doc` github repository. ([#1032](https://github.com/matrix-org/matrix-spec/issues/1032))
- Clarify the format for the Authorization header. ([#1038](https://github.com/matrix-org/matrix-spec/issues/1038), [#1067](https://github.com/matrix-org/matrix-spec/issues/1067))
- Clarify what a "valid event" means when performing checks on a received PDU. ([#1045](https://github.com/matrix-org/matrix-spec/issues/1045))
- Clarify that `valid_until_ts` is in milliseconds, like other timestamps used in Matrix. ([#1055](https://github.com/matrix-org/matrix-spec/issues/1055))
- Clarify that checks on PDUs should refer to the state *before* an event. ([#1070](https://github.com/matrix-org/matrix-spec/issues/1070))
- Clarify the historical handling of non-integer power levels. ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
- Fix various typos throughout the specification. ([#1110](https://github.com/matrix-org/matrix-spec/issues/1110))
- Correct misleading text for `/send_join` response. ([#3703](https://github.com/matrix-org/matrix-spec-proposals/issues/3703))
- Clarify that the `content` for `X-Matrix` signature validation is the parsed JSON body. ([#3727](https://github.com/matrix-org/matrix-spec-proposals/issues/3727))
- Add timestamp massaging as per [MSC3316](https://github.com/matrix-org/matrix-spec-proposals/pull/3316). ([#1094](https://github.com/matrix-org/matrix-spec/issues/1094))
### Identity Service API
No significant changes.
### Push Gateway API
No significant changes.
### Room Versions
<strong>Backwards Compatible Changes</strong>
- Add room version 10 as per [MSC3604](https://github.com/matrix-org/matrix-spec-proposals/pull/3604). ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
- Enforce integer power levels in room version 10 as per [MSC3667](https://github.com/matrix-org/matrix-spec-proposals/pull/3667). ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
- Add a `knock_restricted` join rule supported by room version 10 as per [MSC3787](https://github.com/matrix-org/matrix-spec-proposals/pull/3787). ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
- Update the default room version to 9 as per [MSC3589](https://github.com/matrix-org/matrix-spec-proposals/pull/3589). ([#3739](https://github.com/matrix-org/matrix-spec-proposals/issues/3739))
- Improve readability and understanding of the state resolution algorithms. ([#1037](https://github.com/matrix-org/matrix-spec/issues/1037), [#1042](https://github.com/matrix-org/matrix-spec/issues/1042), [#1043](https://github.com/matrix-org/matrix-spec/issues/1043), [#1120](https://github.com/matrix-org/matrix-spec/issues/1120))
- Improve readability of the authorization rules. ([#1050](https://github.com/matrix-org/matrix-spec/issues/1050))
- For room versions 8, 9, and 10: clarify which homeserver is required to sign the join event. ([#1093](https://github.com/matrix-org/matrix-spec/issues/1093))
- Clarify that room versions 1 through 9 accept stringy power levels, as noted by [MSC3667](https://github.com/matrix-org/matrix-spec-proposals/pull/3667). ([#1099](https://github.com/matrix-org/matrix-spec/issues/1099))
- For all room versions: Add `m.federate` to the authorization rules, as originally intended. ([#1103](https://github.com/matrix-org/matrix-spec/issues/1103))
- For room versions 2 through 10: More explicitly define the mainline of a power event and the mainline ordering of other events. ([#1107](https://github.com/matrix-org/matrix-spec/issues/1107))
- For room versions 7, 8, 9, and 10: fix join membership authorization rules when `join_rule` is `knock`. ([#3737](https://github.com/matrix-org/matrix-spec-proposals/issues/3737))
