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Content on the StackOverflow website often updates without refreshing the screen.
I understand it is using Ajax, so I break out my handy Firebug, and look for the GET requests on the console but there are none (other than asking for similar questions or autosave).
The timer can maybe be just a clock running on the client, but I have seen other updates such as when a new post has been added.
How do they do this?