Should an inclusive tag and a sub-tag be used on the same question?

Question

On the question Is it legal to go take my license plates off a car I sold, without realizing I should keep my plates? there has been some back-and-forth editing on the tags. Specifically texas and united-states were both added, and then united-states was removed again, with some discussion in the comments particularly this comment by Ryan M and this one by Strawberry.

Ryan M maintains that when a question appertains to only a single one of the US states it should use the tag for that state, and not the tag for the US as a whole. Strawberry responds that if one is using tags to filter questions, it is much more helpful to be able to exclude (or include I would add) all us-related posta by using a single tag than having to filter on 52 different ones (each state, DC, and US).

Now the tag description form the united-states tag reads:

For questions specific to the United States as a whole, or that span multiple state jurisdictions. If your question is related to a specific state then you should use that state's tag instead (or as well). (emphasis added)

This seems to permit, but not require, the use of the the united-states tag on questions about the law of a single state. Is, or is not, the use of both tags a good practice?

More generally, where a tag is broad, and another tag refers to a sub-section of its range (say eu and france or criminal-law and trial-procedure) is it a good practice to use both, or only the more restrictive sub-tag? Using the wider tag permits easier filtering and selection, but seems redundant on the question itself. I am honestly not sure, but it might be as well to have an agreed guideline to prevent future disputes, and tell people what they must do in searching and filtering.

I note that a related issue was discussed, but not settled, in Should the tag [united-kingdom] be removed, and replaced with its 4 countries?

There has been an objection to the term "subtag". I meant to indicate any tag whose agreed subject matter is a proper subset of the subject of another tag. Call it a "subset tag" if you like, and call the more inclusive tag a "superset tag".

Answer 1

Tags are non-hierarchical

texas is not in any way a sub tag of united-states. Tags on SE are non-hierarchical. As such a search or filter for one will not find the other.

In order to maximise tag utility, put as many appropriate tags as you can up to the limit of 5. If texas is one of the 5 best tags for the question, use it. If united-states is, then use that.

Each question will stand on its merits as to what the best tags are.

Answer 2

My understanding of the current situation, based on the tag wiki excerpt:

For questions specific to the United States as a whole, or that span multiple state jurisdictions. If your question is related to a specific state then you should use that state's tag instead (or as well).

is that the united-states tag is to be used when the question relates to United States federal law, or, optionally, if it relates to multiple states.

My understanding of (or as well) is that if a question relates to multiple states, one could tag the question with both those states' tags, as well as united-states.

That would not apply to the linked question, which is purely in terms of Texas law. The answers cite Texas law, and would not apply to any other state, as was contended in the comments.

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I'm not opposed to arguments that this should be changed to suggest that both should be tagged, but that seems like it would be hard to consistently enforce, since it would take up at least two of the five tag slots in any question about a specific state. It does make it unfortunate that one can't easily filter for questions about anywhere in the United States, but also Law.SE has little enough traffic that it's pretty practical to read most of them just by opening the front page or the new questions list, even if you only do so every few days (also, I think most of the questions are about things within United States).

The current situation also makes searching for a question for a specific state easier: by searching for that specific state and united-states, you'd get all questions that are specific to your state and to multiple states, rather than every related question about every state.

Answer 3

After reading the various answers, I think that the approved practice should be to use both a subset tag and a superset tag in any and every case where both apply, unless the 5-tag limit does not allow room for both, because of other more relevant tags. Thus in the question that started this, both texas and united-states should be used.

In this comment Ryan argues that the united-states tag should be available for searches specifically about US federal law. But it is already also used for questions that apply to multiple states (as many questions of state law do) where there is no federal law issue. I therefore suggest we create us-federal-law for such questions.

Answer 4

is it a good practice to use both, or only the more restrictive sub-tag?

Including both tags is usually preferable because it allows the user to decide what granularity he wants when doing a search (I for one don't bother reviewing tags except when one or more of them clearly is/are misleading).

The fact that a question relates to just one specific state might matter only when the substance of the law of that state is so different from the rest that using the more inclusive tag would be counterproductive in a search or pointless. However, the reality is that on many issues most of the jurisdictions in the US present significant similarities or overlap in the substance of their laws. At the very least, the more inclusive tag would bring results from which other readers can grasp what elements to bear in mind about their respective jurisdiction.

A non-jurisdictional analogy is the topic of contracts. The tag contract clearly is more inclusive than contract-law, breach-of-contract, and other tags. A question can be very narrow and specifically about breach of contract, but that does not change the fact that it might relevant to readers interested in learning about contracts as a whole. Consequently, there would be no reason for prohibiting contract on questions pertaining to --or tagged with-- breach-of-contract.