matrix-spec/event-schemas/schema/v1/m.room.redaction

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "type": "object",
    "title": "Indicates a previous event has been redacted.",
    "description": "Events can be redacted by either room or server admins. Redacting an event
    means that all keys not required by the protocol are stripped off, allowing
    admins to remove offensive or illegal content that may have been attached
    to any event. This cannot be undone, allowing server owners to physically
    delete the offending data.  There is also a concept of a moderator hiding a
    message event, which can be undone, but cannot be applied to state
    events. The event that has been redacted is specified in the ``redacts``
    event level key.",
    "allOf": [{
        "$ref": "core#/definitions/room_event"
    }],
    "properties": {
        "content": {
            "type": "object",
            "properties": {
                "reason": {
                    "type": "string"
                }
            }
        },
        "redacts": {
            "type": "string"
        },
        "type": {
            "type": "string",
            "enum": ["m.room.redaction"]
        }
    },
    "required": ["redacts"]
}