def ack(messageid, subscriptionid, transactionid=None):
header = '<STR_LIT>' % (subscriptionid, messageid)<EOL>if transactionid:<EOL><INDENT>header += '<STR_LIT>' % transactionid<EOL><DEDENT>return "<STR_LIT>" % header<EOL>
STOMP acknowledge command.

    Acknowledge receipt of a specific message from the server.

    messageid:
        This is the id of the message we are acknowledging,
        what else could it be? ;)

    subscriptionid:
        This is the id of the subscription that applies to the message.

    transactionid:
        This is the id that all actions in this transaction
        will have. If this is not given then a random UUID
        will be generated for this.