Right now, it’s pretty common to have both dnd-3.5e and pathfinder on a question, or dnd-3e and dnd-3.5e.1 In cases such as these, it’s not always clear if the tags are a union (“either-or-or-both”) or an intersection (“only-in-both”).
Personally, I tend to interpret it as:
If it’s a “how do the rules work?” question, the tags are being used as an intersection: the querent wants to know how the rules work in both systems (assuming they are the same, since in these related systems they often are, but a good answer should double-check that and discuss any differences if there are any)
If it’s a “how do I do this within these systems?” question, the tags are being used as a union: any material from either system is acceptable. These still run into problems when the same material is used in both systems (e.g. a recent question tagged dnd-3.5epathfinder was asking about options for a paladin, and I finished my answer only to go back and comment asking “Wait, which paladin are you using?” – I got lucky that time and it was the paladin I’d based my answer on, but it could easily have gone the other way).
I do feel that most users here have similar heuristics, and I do think it mostly goes pretty well. I’m not sure there really is a problem. But I also figure it’s worth a discussion, since there definitely have been times when there was confusion about this and it caused headaches. Should we expect questions with multiple system tags to each define how we are to treat things that differ between them?
- Since D&D 3.5 is supposed to include everything in 3.0 excepting those bits it explicitly updated and changed, in that case part of this question is already answered for us (and often makes the 3.0 tag superfluous).