this attribute is not in the avp, the priority of the presence
document is based on timestamp, so newer documents have higher
priority.
+ * delete_subscription - integer value to give extra control of
+ deleting the subscription after processing of
+ event_route[presence:notify-reply]. If value = 1, it deletes the
+ subscription. If xavp_cfg parameter is set but this attribute is
+ not in the avp, the subscription is not deleted. this does apply
+ for code 404 and 481 where subscription is deleted.
Default value is empty (not set).