"Network-Mom-Stompl-Patterns-Basic.html#t:HB">HB</a></code>, this MVar will be used
                  to keep track of when the heartbeat has actually to
                  be sent.
</li><li> <code>Writer</code> (): The writer through which to send the heartbeat;
                  The queue name of the writer is the registration queue
                  of the registry; note that its type is ():
                  heartbeats are empty messages.
</li><li> <code><a href="Network-Mom-Stompl-Patterns-Basic.html#t: