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I accidentally upvoted a comment and a box appeared. (Since I don't keep a ledger of my votes.) How can I erase the errant vote?
I was afraid to hit the flag icon. Is there a way to tell when I have already voted?
To answer both your questions - an upvoted comment has a highlighted up arrowhead, and clicking on it again gives you a prompt asking you if you want to undo an upvote. You can only undo it once though.