Technically they are two different sites, but there seems to be some clear rules as to when something belongs here or there (is the question about doctrine or just the text)? But suppose someone didn't know where it belonged or their question pertained to both. Could it be cross-posted?
Yes & No. Let me explain.
Cross-posting because you have a question that you don't know where it belongs and so you take a shotgun approach is strongly discouraged.
Cross-posting because you have a question with aspects that are best addressed by a different set of experts and you tailor each version of the question to the best interest of each community is strongly encouraged.
Basically, having a question that could be handled on either site does not excuse you from making the effort to understand the topic matter of each site and doing the background research on the question to ask a good question for each site. Asking questions is hard work, and asking on two sites is easily going to be twice as much work. Copy/pasting the same question isn't going to cut it. It's going to get shut down one place or the other, possibly both.
A recent example of this would be this question about the Jerusalem Bible. It got closed as Not Constructive on both sites. It really wasn't a good match for either, but there were aspects of it that could work on both. I have edited and reopened it on C.SE and now I think it's a reasonable question for the expects of this community. Thanks to Jon the variant of the question on BH has been edited to make it a constructive question for that set of experts. Now, rather than a double-posted shotgun question, we have two targeted questions on a related topic that can be addressed by the appropriate experts in church practice/history/doctrine and in textual issues.
From this example it should be apparent how a question on the same topic can be tailored for each site, but the different expertise sets that we cater to should not be approached with a drag net.
I'm in agreement with Caleb, as usual. Targeted cross-posts are not just ok, but encouraged.1 I'd like to take this opportunity to propose a question triage procedure:
If the question is junk (and we've all seen junky questions) pick one2 or more of the following actions:
- vote (or flag) to close
Questions that are on-topic for another site should be migrated within 60 days. In this case:
Questions that are even partially on-topic for this site should be allowed to develop here. Even if the question might find an audience on another site, I've come to the conclusion that there's no immediate need to point the asker somewhere else. Unless the question is a candidate for migration, it can even cause problems. Instead, it's probably better to wait until the question has gotten cold and then suggest that the asker target a question to Biblical Hermeneutics. Alternatively, feel free to ask the question in your own words at the other site and link to that question in the comments (or your own answer). It's pretty unlikely that the user who has asked a question that only partially is on-topic will be able to ask an on-topic question on a totally different site.
When similar or related questions are asked on both sites, try to link them up in the form of comments on all the questions. For reference, links in comments are managed thusly:
[Title of question to be linked to](http://X.stackexchange.com/q/... "Optional comment")
At this point, it's probably best to think of Christianity.SE and Biblical Hermeneutics as completely different sites that are only tangentially related. As always, respect the community.
My favorite example of quality cross-posting is:
Did Jephthah have pets? (Biblical Hermeneutics)
What else could have come out of Yiftach's house? (Mi Yodeya)
Did Jephthah actually sacrifice his daughter? (Biblical Hermeneutics)
Did Jephthah sacrifice his daughter? (Christianity)
Not only are there some excellent answers represented, we can see the issue through several different lenses.
I've more or less lost patience with the "Hey! What's with the downvotes on my question!?!" comments. Sometimes I feel like I put in more research to explain my downvote than the asker put in to write the question. Explaining a vote to close might be more important, but mostly for other readers and not so much for the asker.
If you want to ask the same question and get "answers" in different contexts, then yes. For example, I may ask a question regarding the Old Testament here and also on Judiasm.SE. Similarly, even though they're sister sites (somewhat unfortunate), if I wanted to get a meaning regarding a passage in the Christian context or more of a hermeneutic answer, I may recommend the use of both.