MSC1695 Message Edits

proposals/1695-message-edits.md

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+Proposal
+========
+
+I propose for message edits to follow a similar format to replies, using  `m.relates_to`.
+The content of the edited message should be inside `m.replaces.new_content` which can
+be accessed if the client is edit-aware. If the client is not aware, it can use `content.body`
+and `content.formatted_body` to render an approximation of the edit. The fallback should be
+in the format given below.
+
+Clients should always favour fetching the source from `m.replaces.event_id` where possible,
+rather than using the fallback as the fallback can be faked. Furthermore, clients should refuse
+to display with an appropriate message when the sender of the source event and the edit event differ.
+
+It should be noted that this allows any event to be replaced by an entirely different set of content.
+The client should make a best effort attempt to describe the relationship between the two events for
+both the fallback and representation.
+
+If the edit event's content is invalid, it is acceptable to display/keep the old event in place with a warning.
+
+User should be warned that editing an an
+
+Example
+-------
+
+Original message:
+```javascript
+{
+  "content": {
+    "body": "This is an example message I want to edit.",
+    "msgtype": "m.text"
+  },
+  "event_id": "$1539340060524DGxMc:half-shot.uk",
+  "sender": "@Half-Shot:half-shot.uk",
+  "type": "m.room.message",
+  "room_id": "!IPcexxPYNJKmTvRfoV:half-shot.uk"
+}
+```
+
+New edited message:
+```javascript
+{
+  "content": {
+    "body": "Edited: ~~This is an example message I want to edit~~ This is the edited message",
+    "format": "org.matrix.custom.html",
+    "formatted_body": "Edited: <del>This is an example message I want to edit</del> This is the edited message",
+    "m.relates_to": {
+      "m.replaces": {
+        "event_id": "$1539340060524DGxMc:half-shot.uk",
+        "new_content": {
+            "body": "This is the edited message.",
+            "msgtype": "m.text"
+        }
+      }
+    },
+    "msgtype": "m.text"
+  },
+  "event_id": "$1539340066525PiiWI:half-shot.uk",
+  "sender": "@Half-Shot:half-shot.uk",
+  "type": "m.room.message",
+  "room_id": "!IPcexxPYNJKmTvRfoV:half-shot.uk"
+}
+```
+
+Problems
+--------
+
+Clients will also render the original event without the edit if the client isn't aware of
+the edited event since event aggregations aren't a thing yet. This is considered an
+acceptable risk for this proposal and aggregations are considered an extension to
+message edits for Matrix.
+
+It should be noted that many bridges and bots already show edits in the form of a
+fallback already, so this event only strives to add some specced metadata to allow
+clients to render them clearly.In the future, this proposal could be extended to
+use aggregations to show a list of edits made to a message.