This discussion is inspired by Magus Spell Scars. The question doesn't clearly state which system it uses in the text, which is normally a case of Don't guess the system. But the author tagged the question with magus, whose tag wiki excerpt reads:
Pathfinder class that blends martial prowess with spell casting, from the book Ultimate Magic.
This tag describes the system, even the book, that the question is about. In my opinion a tag that describes a system is a system-tag and should suffice to exclude all other options of what the question could be about.
If we don't trust users to correctly tag their questions with such a specific tag, why would be trust them when they use a more generic tag such as pathfinder?
The problem is that we are requiring everyone to tag their question with a system, but there is no clear definition of "system-tag". It seems to be "general tag about a system", which in my eyes makes the magus tag a bad tag.
What should we do in such a situation? Leave the question and ask the OP to choose from a narrow yet-to-define list of "system-tag"? Add the generic "system-tag" because the OP already defined a subset of the system that the question is about?
Or is this simply an example of a bad tag and we should either change the tag wiki to be more generic or change the tag name to be specifically about the system (for example: pathfinder-magus)?