Unifier data mapping for P6

I am currently configuring  the integration between P6EPPM and Unifier, both version 16.1 I am using the OOTB integration feature to pass elements from P6 to Unifier. Unifier has a Tag element in the data mapping option, I want to use this element to pass Key Milestone values. In P6, there is no Tag element. I attempted to use Activity code or UDF but cannot get data to map. Which P6 element can I use to map to the Unifier Tag element. I am using xml mapping. Note: I am not using GATEWAY. Is there any standard mapping list, which