MSC2414: Make reason and score parameters optional for reporting content

proposals/2414-optional-content-reporting-reason.md

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+# MSC2414: Make `reason` and `score` optional for reporting content
+
+## Proposal
+
+On the [report content endpoint](https://matrix.org/docs/spec/client_server/r0.6.1#post-matrix-client-r0-rooms-roomid-report-eventid)
+we remove the `required` flag for both the `reason` and `score` parameters, as
+well as the "may be blank" clause in the description of `reason`.
+
+## Rationale
+
+### `reason` Parameter
+
+Currently, the spec says that the `reason` parameter on the content reporting
+endpoint is required, but also says that the string "may be blank." This
+seems to be a contradiction.
+
+Note that the kicking and banning endpoints already have optional `reason`
+parameters. The other membership endpoints mentioned in
+[#2367][membership-endpoints] will also add optional `reason` parameters,
+so it would be more more consistent with the rest of the spec to make this
+optional as well.
+
+### `score` Parameter
+
+The spec also requires the `score` parameter, but its usefulness is limited.
+Offensiveness is difficult to measure and is likely not going to be applied
+consistently across several rooms. Because of this ambiguity, it seems, many
+clients [simply hard-code the integer value][hard-code].
+
+To make this useful, for example, room administrators would need a way to map more
+specific values to the integer range and perhaps even instruct the client to
+display those mappings to the user. That may be possible to do in a closed
+client/homeserver implementation, but not generally across the Matrix protocol.
+
+Making `score` optional would enable this feature to be used in specific contexts
+while not forcing clients to support the ambiguity it brings.
+
+## Backwards Compatibility
+
+Since servers currently expect these fields to be sent by all clients, making
+them optional is a breaking change. Clients should check the spec versions
+the homeserver supports to detect this change.
+
+[membership-endpoints]: https://github.com/matrix-org/matrix-doc/pull/2367
+[hard-code]: https://github.com/matrix-org/matrix-react-sdk/pull/3290/files#diff-551ca16d6a8ffb96888b337b5246402dR66