[WIP] MSC4298: Room version components for 'Redact on ban'

proposals/4298-redact-on-ban-room-version.md

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+# MSC4298: Room version components for 'Redact on ban'
+
+[MSC4293](https://github.com/matrix-org/matrix-spec-proposals/pull/4293) introduces a capability to
+redact a sender's events upon being kicked or banned in the room. This functionality can operate in
+existing room versions, but can be improved in a future room version to be more reliable.
+
+This proposal covers the parts which require a room version, allowing MSC4293 to progress more quickly
+through the process, protecting existing (and non-conflicting) room versions. Namely, this proposal
+adjusts the redaction algorithm to protect the `redact_events` field from redaction itself.
+
+**WIP Note**: This proposal may expand in scope as more room version-affecting functionality is
+discovered/desired.
+
+## Proposal
+
+In a future room version, the [redaction algorithm](https://spec.matrix.org/v1.14/rooms/v11/#redactions)
+is modified to retain `redact_events` on `m.room.member` events.
+
+## Potential issues
+
+None expected - this proposal resolves a potential issue highlighted in MSC4293.
+
+## Alternatives
+
+None relevant.
+
+## Security considerations
+
+None relevant - see potential issues section.
+
+## Unstable prefix
+
+While this proposal is not incorporated into a stable room version, implementations should instead
+use `org.matrix.msc4298.v1` based upon [room version 11](https://spec.matrix.org/v1.14/rooms/v11/).
+
+## Dependencies
+
+This MSC requires [MSC4293](https://github.com/matrix-org/matrix-spec-proposals/pull/4293) to be
+functional.