matrix-spec-proposals/event-schemas/schema/v1/m.room.message#m.emote

{
    "type": "object",
    "title": "EmoteMessage",
    "description": "This message is similar to ``m.text`` except that the sender is 'performing' the action contained in the ``body`` key, similar to ``/me`` in IRC. This message should be prefixed by the name of the sender. This message could also be represented in a different colour to distinguish it from regular ``m.text`` messages.",
    "allOf": [{
        "$ref": "core-event-schema/room_event.json"
    }],
    "properties": {
        "content": {
            "type": "object",
            "properties": {
                "msgtype": {
                    "type": "string",
                    "enum": ["m.emote"]
                },
                "body": {
                    "type": "string",
                    "description": "The emote action to perform."
                }
            },
            "required": ["msgtype", "body"]
        },
        "type": {
            "type": "string",
            "enum": ["m.room.message"]
        }
    }
}