A recent question in the meta addressed whether cross-system questions should ever be combined if the answer to both questions was determined to be the same.
I understand (and agree with) the answers posted in response, but it made me wonder what the tagging policy on such a question would be. If I asked "How does {Generic Mechanic that's identical between 3.5 and Pathfinder} work?"* would it be best to tag that question as a 3.5 question, a Pathfinder question, both, or apply no system tag what so ever?
*Please assume such a question exists and is valid, unless issuing a frame challenge that such questions inherently cannot exist.