Prologue: I am going to be using the Theoretical Computer Science as an example. I posted my question here because I believe my question is of a general nature. I am not picking on TCS in any way.
Tag taxonomy consumes a great deal of time on Meta.StackOverflow, particularly when dealing with Stack Overflow specifically. In the process of asking my question, I hope the reasons why become clear.
One of the things I have the most difficulty with when I visit a new Stack Exchange site is figuring out how the tag system works on that particular site. In my experience, I have found that every site has radically different philosophies with respect to tagging, so your tagging skills are not transferable from site to site. I still have this problem on Meta; in fact, you will see that someone will come along shortly and fix my tags for me, on this very question.
Today I stumbled into a question on Theoretical Computer Science, and noticed that the question I was looking at was tagged
cc.complexity-theory. I wondered, "How does that work? What does
cc mean? So I went to the Help Center, and found the Tagging article, but it doesn't say anything about these prefixes.
I then put [tags] in the search box on their Meta site, but didn't find anything that stood out. I thought, "Well, these are post-graduate types; I bet they have their own FAQ." Sure enough, it is here. That post led me to this answer, which immediately hits me with the term, "arXiv tags."
Hmm. What's an arXiv tag?
Right below that, there's an inscription that says: "[FIXME: add answer]". OK, I guess it's under construction. Well, it turns out that there's a supplemental FAQ with a similar "How do I tag" link in it, except this one links to
Well, OK, that link was also right below the "Under Construction" sign. In any case, this post describes what arXiv tags are for, but doesn't establish any community consensus. If anything, there's mostly dissent there.
And I still don't know what an arXiv tag is.
So here's my question. How are new users expected to know how to properly tag questions? What is the canonical resource that we can steer them to that will help them answer the question: "How do we properly tag on this site?