If an answer answers concerns posed in the question, and/or the question posed in the body, but does not answer the question as posed in the title, is it an acceptable answer?
I want to note that usually this isn't a problem. Most of the time the title question will reflect the question body pretty well. A complete answer will be certain to address the question asked in both the title and body.
When they conflict, my general rule is, unless the question body doesn't actually contain a question, I defer to the question body. And when there is no actual question in the body, I encourage the OP to edit the body to explain their question.
There have been many occasions where people do a poor job of explaining their question in the title. Ignoring the body of the question to merely answer the question in the title is unlikely to help the person asking the question in the case you describe.
For example, we very often get people asking things like
Can I substitute rice milk for whole milk?
A good percentage of the time, they're actually asking the opposite question. We try to edit these question titles to reflect what they describe in the question body but we don't always manage it.
Other times, the title question is an absurdly broad version of the question... to use the example above, the "correct" answer probably depends heavily on what you're doing with it. So, while the answer may be "yes" in some cases, ignoring the specific case in the question's body, which may actually be a "no" is bad.
I like to think of it this way - we have question titles to give people a general overview of the question but we rely on the body to be more specific because titles should be relatively brief.
Ignoring the question body leaves you open to downvotes and (in the case of an answer that ends up not answering the question at all, regardless of the title) a deleted answer.
I don't think comparing title vs body is particularly useful. They're both important; it's acceptable to write partial answers that address only one important part of a question, but it's best to address the whole question.
I've seen a few common cases:
- The title and body conflict: they're different questions, and a single person is likely only to ask one of the two. In this case, get clarification before answering, probably by asking the OP. (In some cases you can figure out what they actually meant, and edit yourself.)
- The title includes a question that's not in the body, but the two make sense together. This happens when people are a bit careless; most likely, they figured that since they put something in the title, they don't need to put it in the body. A good answer will address both the title and the body. (A partial answer could address one or the other, but it'd be a partial answer - acceptable, but not as good.)
- The same question is phrased a bit differently in the title and body. This is pretty much just the easy version of the previous bullet: take the title and body together to understand what the OP is asking.
Bottom line, this is really not much different from asking "what do we do if there are two different questions in the body?" The answer is, unsurprisingly, figure out what the OP wanted to ask and then address it - all of it, preferably.
Sure, it's acceptable to write partial answers, in that they probably won't get a lot of downvotes, and shouldn't get deleted. But "acceptable" is a low bar. Being able to "get away" with a partial answer doesn't mean that the aspect of the question you didn't cover wasn't important, and people may well downvote answers they think overlooked an important part of the question.