I would quite disagree with Dom's answer that limits it to either official word or "commonly accepted" interpretations (by the way, what's "commonly accepted" anyway?). Not because I think proper sources or established interpretations are evil, of course they aren't, but because I think there can very well be to a large degree objectively assessable value in rather unprecedented interpretations as well, if presented with reasonable arguments.
This does of course not mean that any kind of personal rambling is justified, but rather that you can very well back your own theory in a more or less objective and reasonable way, be that with proper references to the song, its artist, the cultural background of its development, ... Just favour the why over the what. Of course this won't necessarily make it the 100% correct answer, but it can very well make it a good answer and it doesn't mean that the post magically degrades into a "discussion forum". Afterall just limiting the answers to something everyone has already agreed on anyway seems rather narrow, we're not just a Wikipedia copy here and lyrics/song analysis seems to be a very engaging, interesting and perfectly fitting topic for this site, especially when the possible answers are not only an interview or Wiki quote (of course those aren't bad answers either, but shouldn't be the only ones allowed).
(This comes from someone who frequents another SE site with an IMHO similar subject and who always enjoys good analysis questions/answers if they're well-reasoned.)