Negative acknowledge of one or more messages. If `multiple` is set to `true`, all messages up to the one specified by `delivery_tag` are considered as not acknowledged by the server. If `requeue` is set to `true`, the message will be returned to the queue and redelivered to the next available consumer. This is a RabbitMQ specific extension to AMQP 0.9.1. It is equivalent to reject, but allows rejecting multiple messages using the `multiple` option.