with this option set, if this client publishes to a topic to which it is subscribed, the broker will not publish the message back to the client.
with this option set, messages published for this subscription will keep the retain flag as was set by the publishing client.
with this option set, pre-existing retained messages are sent as soon as the subscription is made, even if the subscription already exists.
with this option set, pre-existing retained messages will never be sent for this subscription.
with this option set, pre-existing retained messages for this subscription will be sent when the subscription is made, but only if the subscription does not already exist.