Merge 72b34b863f into 65b1db721d

We seem to have [updated this for m.room.name](https://github.com/matrix-org/matrix-spec/pull/1639) some years back but omitted it for topic.

changelogs/client_server/newsfragments/2068.clarification

@@ -0,0 +1 @@
+Clarify behaviour when the `topic` key of a `m.room.topic` event is absent, null, or empty.

changelogs/client_server/newsfragments/2077.clarification

@@ -0,0 +1 @@
+Fix the example of the `GET /sync` endpoint and the `m.room.member` example used in several places.

changelogs/server_server/newsfragments/2067.clarification

@@ -0,0 +1 @@
+Add a note to the invite endpoints that invites to local users may be received twice over federation if the homeserver is already in the room.

data/api/client-server/sync.yaml

@@ -441,17 +441,57 @@ paths:
                           "state": {
                             "events": [
                               {
-                                "$ref": "../../event-schemas/examples/m.room.member.yaml"
+                                "content": {
+                                  "avatar_url": "mxc://example.org/SFHyPlCeYUSFFxlgbQYZmoEoe",
+                                  "displayname": "Example user",
+                                  "membership": "join"
+                                },
+                                "event_id": "$143273976499sgjks:example.org",
+                                "origin_server_ts": 1432735824653,
+                                "sender": "@example:example.org",
+                                "state_key": "@example:example.org",
+                                "type": "m.room.member",
+                                "unsigned": {
+                                  "age": 45603,
+                                  "membership": "join"
+                                }
                               }
                             ]
                           },
                           "timeline": {
                             "events": [
                               {
-                                "$ref": "../../event-schemas/examples/m.room.member.yaml"
+                                "content": {
+                                  "avatar_url": "mxc://example.org/SEsfnsuifSDFSSEF",
+                                  "displayname": "Alice Margatroid",
+                                  "membership": "join",
+                                  "reason": "Looking for support"
+                                },
+                                "event_id": "$143273582443PhrSn:example.org",
+                                "origin_server_ts": 1432735824653,
+                                "sender": "@alice:example.org",
+                                "state_key": "@alice:example.org",
+                                "type": "m.room.member",
+                                "unsigned": {
+                                  "age": 1234,
+                                  "membership": "join"
+                                }
                               },
                               {
-                                "$ref": "../../event-schemas/examples/m.room.message$m.text.yaml"
+                                "content": {
+                                  "body": "This is an example text message",
+                                  "format": "org.matrix.custom.html",
+                                  "formatted_body": "<b>This is an example text message</b>",
+                                  "msgtype": "m.text"
+                                },
+                                "event_id": "$143273582443PhrSn:example.org",
+                                "origin_server_ts": 1432735824653,
+                                "sender": "@example:example.org",
+                                "type": "m.room.message",
+                                "unsigned": {
+                                  "age": 1234,
+                                  "membership": "join"
+                                }
                               }
                             ],
                             "limited": true,

data/api/server-server/invites-v1.yaml

@@ -20,7 +20,7 @@ paths:
     put:
       summary: Invites a remote user to a room
       description: |-
-        Invites a remote user to a room. Once the event has been  signed by both the inviting
+        Invites a remote user to a room. Once the event has been signed by both the inviting
         homeserver and the invited homeserver, it can be sent to all of the servers in the
         room by the inviting homeserver.
 
@@ -32,6 +32,10 @@ paths:
         [room version specification](/rooms) for precise event formats. **The request and response
         bodies here describe the common event fields in more detail and may be missing other
         required fields for a PDU.**
+
+        Also note that if the remote homeserver is already in the room, it will receive the
+        invite event twice; once through this endpoint, and again through a [federation
+        transaction](https://spec.matrix.org/v1.13/server-server-api/#transactions).
       operationId: sendInviteV1
       security:
         - signedRequest: []

data/api/server-server/invites-v2.yaml

@@ -24,7 +24,7 @@ paths:
         This API is nearly identical to the v1 API with the exception of the request
         body being different, and the response format fixed.
 
-        Invites a remote user to a room. Once the event has been  signed by both the inviting
+        Invites a remote user to a room. Once the event has been signed by both the inviting
         homeserver and the invited homeserver, it can be sent to all of the servers in the
         room by the inviting homeserver.
 
@@ -36,6 +36,10 @@ paths:
         [room version specification](/rooms) for precise event formats. **The request and response
         bodies here describe the common event fields in more detail and may be missing other
         required fields for a PDU.**
+
+        Also note that if the remote homeserver is already in the room, it will receive the
+        invite event twice; once through this endpoint, and again through a [federation
+        transaction](https://spec.matrix.org/v1.13/server-server-api/#transactions).
       operationId: sendInviteV2
       security:
         - signedRequest: []

data/event-schemas/examples/m.room.member.yaml

@@ -1,6 +1,7 @@
 {
   "$ref": "core/state_event.json",
   "state_key": "@alice:example.org",
+  "sender": "@alice:example.org",
   "type": "m.room.member",
   "content": {
     "membership": "join",

data/event-schemas/schema/m.room.topic.yaml

@@ -1,7 +1,14 @@
 ---
 allOf:
   - $ref: core-event-schema/state_event.yaml
-description: 'A topic is a short message detailing what is currently being discussed in the room.  It can also be used as a way to display extra information about the room, which may not be suitable for the room name. The room topic can also be set when creating a room using `/createRoom` with the `topic` key.'
+description: |- 
+    A topic is a short message detailing what is currently being discussed in the room.
+    It can also be used as a way to display extra information about the room, which may not
+    be suitable for the room name.
+    The room topic can also be set when creating a room using `/createRoom` with the `topic` key.'
+    
+    If the `topic` property is absent, null, or empty then the topic is unset. In other words,
+    an empty `topic` property effectively resets the room to having no topic.
 properties:
   content:
     properties: