Consider an early Christian letter that is not typically included in the Bible: Polycarp to the Philippians. It contains many quotations from writings that are clearly on-topic for the site. The letter is invaluable for informing us of the state of Christian texts at the time of its writing. (There's even a database of cross-references, which can be quite useful.) For instance, we can potentially better understand 1 Timothy 6:10 by bringing in evidence from Polycarp.
But Polycarp's letter is not itself in the scope of the site with a few narrow exceptions:
- We might consider the way that Polycarp uses biblical texts to ask a question about hermeneutical approaches.
- We might think of Polycarp as a translation of the snippets of biblical text it quotes. (This would be more plausible for his quotations of Hebrew scripture since the letter is in Greek.)
- We might want to ask about whether Polycarp helps us understand the source of biblical texts.
The bulk of questions on this site are interpretation questions: "What does this passage mean?" If "this passage" is specifically the text of Polycarp's letter, I'd argue the question is off-topic for this site. (Though there might be interest in Christianity.SE.) The three exceptions I listed (and thinking about it, there might be room to considers historical context too) allow this extra-biblical text to be the subject of the question because it serves as a proxy for questions about how we can understand the biblical texts which are the topic of the site.
The question on main that seems to have sparked this meta question is a useful example. The question is directly about the Joseph Smith Translation, but the question behind the question is really about John 4:24. Did the translator use evidence from manuscripts we have access to today?
Now I have a somewhat dim view of the usefulness of The Pearl of Great Price and other texts produced by Joseph Smith and his contemporaries. It seems possible to crank out endless variations of the question with similar answers. I don't think that's particularly useful or interesting. But occasional questions do seem worth asking if they bring something unique.
I should also note that texts (such as Polycarp's letter) that are closer chronologically to the biblical texts are likely to be a better source of on-topic questions than texts far removed (such as Joseph Smith's output).
Responses to comments
I sought a logically consistent standard for which portions of the PoGP are in and out of scope for the site - do I correctly surmise that you believe a clear standard on this matter is unattainable?
No. It's pretty clear to me that the Pearl of Great Price is not a biblical text for the purposes of this site. It's not profitable to divide the text into in-scope and out-of-scope sections for the same reason it isn't possible to do that with Polycarp's letter. Either a text as a whole is "biblical" (in the context of this site) or it is not. At this point, the question of which texts are included seems pretty settled. It would require some discussion on Meta and some form of consensus to expand the list.
That said, it is possible to ask about a non-biblical texts in an ancillary manner, as I explained above.
How is "I have a somewhat dim view of the usefulness of The PoGP..." related to the OP? I recognize that most users of this site a) have a dim view of the PoGP & b) have not studied it, but this is not what I'm asking about. Since the Q behind the Q behind this Q was a disagreement on CSE, I asked for the very reason you outlined: "It seems possible to crank out endless variations of the question" - I'd rather avoid that. If we want to use the site as a force-multiplier for contempt for non-Biblical texts, we're merely limiting the diversity of thought we will see on the site. Why do that?
Generally speaking, the scope of one site is decided by the people within that's site's community and isn't dictated by some other site's scope. Obviously we should avoid overlap and strive to have a home for as many questions as possible. But that's a secondary goal. The important thing for this site is that questions asked here are of interest to this community.
My dim view of Pearl comes not from any preexisting theological position. Instead it comes from looking at how the text was produced and what it contains. In particular, it was published centuries after the texts this site considers in-scope based on a misinterpretation of Egyptian papyri, among other problems.
This why I considered Polycarp instead. His letter was produced contemporaneously with biblical texts and he appears to have access to very early Greek manuscripts. His paraphrasing and interpretation of biblical texts reflects someone who understands the original language (because he used it himself). Polycarp to the Philippians has a much better claim to being on-topic here, but it falls short.