Why message body is of type string https://github.com/queue-interop/queue-interop/blob/master/src/Message.php#L19? How can I send objects inside of message body? I need to double encode it? It is weird.

Java specification definitily says that body can be an object, a stream and so on https://docs.oracle.com/javaee/7/api/javax/jms/Message.html