This is one of Stackexchange's important Beta questions. So what shall we have?
Brief outline of the documentation:
Who should use this site? Who is the audience?
What should be specifically Not Allowed on the site? More specifically, what are the stupid quirky questions that we shouldn't answer 500,000 times?
What is a good description of the questions we can answer on the site?
There's been discussion of this under various topics on Meta. I want to make a few broad observations to start pushing things in a more concrete direction.
My personal view is that we should not include people looking for legal help or advice within our explicit target audience. I would prefer this site to be analogous to StackOverflow rather than Super User: technical discussion between people active or interested in the field (whether professional or amateur), rather than a forum for end-user support. I think I'm in the minority here.
Attracting genuine experts is going to be an enormous boot-strapping problem. I've been relatively active because I'm in a pretty unusual position: (1) I'm an experienced programmer so I'm familiar with the benefits of a StackOverflow-type service; (2) I'm in the midst of studying for the bar exam, so a lot of things are "on topic" for me in a way they won't be in a few months; and (3) I'm not (yet) trying to make my billable hours targets, and my opportunity cost is relatively low, especially when I can justify things as "bar review." With a few exceptions, my sense is that the majority of trained lawyers are in exactly the opposite situation: they have no reason to expect any professional value from the site; most of the questions will be irrelevant to their interests (and there are other reasons not to write about their core topics); and they've got pretty high opportunity costs.
The above two observations are mutually reinforcing: lawyers will be less interested in a consumer-oriented site, and a consumer-oriented site will be less useful in the absence of lawyers.
That said, I think there are a few areas where this site will be potentially very productive even in the short term.
This is a good forum for answering the sorts of questions that librarians answer. Most prominently, helping people find laws, cases, and other resources. Right now, this sort of online resource is widely dispersed, most notably on various law schools' library websites. Both lawyers and end-users can benefit from this, and the dangers of being "wrong" are relatively low, except with answers like "no, there's no law prohibiting that," which are easy to avoid and censure.
We can also productively explain specific statutes, cases, etc. I have in mind translating legalese into plain English. Right now a lot of the resources in this area are bad, wrong, or hopelessly over-technical. Resources for law students would fit in here as well; much as I hate case briefs, I suspect we can constructively answer questions asking for explanations of one aspect of a particular case. And we'll likely be able to attract enthusiastic law students to write such answers: it'd be good writing practice for them.
[This is not an exhaustive list of what I think we can do productively; I just ran out of time to work on this answer.]
Don't mean to pick on one user, but this one offers a lot of great examples of how not to phrase questions.
Since the site will attract people embroiled in legal problems we should probably say something like:
Questions should be phrased impersonally, and should be limited to one subject per question.
If you have a personal legal problem please re-read the preceding sentence. Don't write an epic account. Don't share details that don't inform the subject of your question. Skip the justifications, arguments, and gripes that paint you as the victim or good guy. You might be on trial, but you're not on trial here. Also, nobody here offers legal advice. If you don't ask a generic question you'll probably just be told to consult a lawyer.
Example, Bad version:
I went to the police asking for help with a tenant. The cop asked me to follow him to his office where he was "going to take my side of the story." I was involuntarily detained there for hours. They denied my needed eye medications and that denial has created permanent damage to my left eye. The cops charged me with Criminal Trespassing in the building where I lived. How do I proceed from here with a complaint about this action?
Example, OK version:
In the United States, if the police detain me and deprive me of medical assistance during detention, resulting in some permanent injury, what redress do I have under the law?
I think we'll see law students and laypersons be the main users of the site - perhaps, if we're lucky, some legal academics. I agree with Christian that we're unlikely to have practising legal professionals active here.
I've commented on a related answer, but: a resource list for those people asking the questions we might get a million times might be useful.
ELL.meta has a resource list, for instance.
Maybe something similar would be useful? Links to case citators, databases, etc...
As a law practitioner to me this ia a very philosophical question. Law cannot and should not be handled by amateurs. Asking for guidance on how to interpret law reqires knowlegde within the area by the correspondent as the consequences of aiding faulty advice could be enormous. That said, it must also be clear to anyone that legal advice must be given by professionals - no one should ever treat answers given here as legally sustainable.
I think the documentation given here should be of an academic nature. One of the biggest strengths of the Stack Exchange community is it's purpose of serving as a platform for knowledge growth. As our world expands and becomes more complex legislators tend to increase legal regulations in almost every area of life. This demands greater participation by each and everyone of us in discussing the ethics and moral behind our laws. This is what I would like this corner of Stack Exchange to be all about; a place to ask, answer, clarify, discuss, comment and challenge current views on the reasoning behind the laws.
I would also like to expand @feetwets argumentation: Unarguably this site (not Meta) will attract people facing legal problems whom most certainly will ask for advice on how to solve them - perhaps even asking for the right interpretation of law. Members joining this site need to be aware of the severity of engaging in answers that aren't legally solid. As a legal practitioner this is obvious but for non-professionals it might be tempting to advice someone based on a gut feeling. Therefore I would suggest that the community monitor any attempt to advice authors legally and then act on those attempts properly.
I'd like to round up this answer by acknowleding the founders of Law.SE. I've been looking forward for this site to run into Beta for a very long time and I'm glad to see it finally did. There are so much for me to learn on the matter of international law by following this site.
