Sharing lottery winnings

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Let's suppose your spouse (or committed partner) wins a modest amount of lottery money from a ticket they purchased. It's not quit jobs and buy a mansion millions — let's say somewhere between 2,000 - 20,000.

Is it their money or "our" money? Is it "extra" money they can spend on a impractical dream item, or is it a windfall that should be put towards bettering your joint financial situation?