"mode": {
      "description": "Mode of activation: immediate (on message receipt), scheduled_absolute (when internal clock >= requested_time), scheduled_relative (when internal clock >= time of message receipt + requested_time), or null (no activation scheduled).",
      "anyOf": [{
        "type": "string",
        "enum": [
          "activate_immediate",
          "activate_scheduled_absolute",
          "activate_scheduled_relative"
        ]
      }, {
        "type": "null"
      }]
    }