Merge pull request #1983 from matrix-org/travis/msc/leave-reason

MSC1983: Supporting a reason for leaving rooms

proposals/1983-leave-reasons.md

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+# Proposal to add reasons for leaving a room
+
+This proposal intends to solve [#1295](https://github.com/matrix-org/matrix-doc/issues/1295). Currently
+people can be kicked from a room for a human-readable reason, but when voluntarily leaving the `reason`
+is not considered. 
+
+## Proposal
+
+Like when kicking someone, `m.room.member` events with `membership: leave` can have a string `reason`.
+The reason is a human-readable string of text which clients should display to users of the room, providing
+users with the ability to leave a room for a reason of their choosing. The field is optional.
+
+Having such a field gives Matrix better compatibility with other networks such as IRC which use the leave
+reason to communicate connection problems ("ping timeout", etc). Although Matrix doesn't have a need for a
+persistent connection to remain in the room, having a reason can improve the bridge experience.
+
+An example of a partial leave event with reason would be:
+```json
+{
+  "type": "m.room.member",
+  "sender": "@travis:t2l.io",
+  "state_key": "@travis:t2l.io",
+  "content": {
+    "membership": "leave",
+    "reason": "I'm in too many rooms and never talk here"
+  }
+}
+```
+
+
+## Potential issues
+
+There is a chance that quality of communication may deteriorate as a result of adding this field. Arguments
+in rooms may result in the leave reason having personal attacks against other room members or rude remarks.
+Moderators would be expected to handle these situations for these cases, including redacting the state event
+if needed.
+
+This also opens up an avenue for spam by having a very large reason for leaving. Clients are encouraged to
+trim/hide the reason at a reasonable length.