matrix-spec/event-schemas/schema/v1/core/state_event.json

{
    "$schema": "http://json-schema.org/draft-04/schema#",
        "type": "object",
        "title": "State Event",
        "description": "In addition to the Room Event fields, State Events have the following additional fields.",
        "allOf":[{
            "$ref": "core/room_event.json"
        }],
        "properties": {
            "state_key": {
                "type": "string",
                "description": "A unique key which defines the overwriting semantics for this piece of room state. This value is often a zero-length string. The presence of this key makes this event a State Event."
            },
            "prev_content": {
                "type": "object",
                "description": "Optional. The previous ``content`` for this event. If there is no previous content, this key will be missing."
            }
        },
        "required": ["state_key"]
}