I am looking for a complete documentation on what all stackoverflow supports or provides in terms of its features?
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I do not believe there is a single feature list or design document available to detail all the features of StackOverflow. Most of that information can be found by perusing the various SOFAQ-tagged posts on StackOverflow. This will give you a very detailed run-down of the way things work and the way the community is set up to perform.
I bet Joel would like that too! Eventually you'll get one, when they try selling it (maybe. I would expect it, but then again, maybe they won't care), but until then your best bet is just scrounging around.