The PriorityLabel with DataType String specifies the priority of the according sender. The network stack will use the PriorityLabel to look up the priority settings for the transport protocol headers.
The priority labels defined by OPC UA should have the following form:
Example values are "opc.qos.lbl://low" or "opc.qos.lbl://high". The mapping is described in 22.214.171.124.
Note: This version does not define concrete labels. The engineering process needs to provide them and also build up the PriorityMappingTable in OPC 10000-22 accordingly.