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

{
    "type": "object",
    "title": "Redaction",
    "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-event-schema/room_event.json"
    }],
    "properties": {
        "content": {
            "type": "object",
            "properties": {
                "reason": {
                    "type": "string",
                    "description": "The reason for the redaction, if any."
                }
            }
        },
        "redacts": {
            "type": "string",
            "description": "The event ID that was redacted."
        },
        "type": {
            "type": "string",
            "enum": ["m.room.redaction"]
        }
    },
    "required": ["redacts"]
}