One event notification. :source and :data hold the message's SimpleItem name/value pairs.
:source
:data
SimpleItem
@type t() :: %ExOxvif.Events.Message{ data: %{required(String.t()) => String.t()}, property_operation: String.t(), source: %{required(String.t()) => String.t()}, topic: String.t(), utc_time: String.t() }