**coin selection is the process that describes how the algorithms driving Bitcoin choose which of your Bitcoins to spend when you approve a spending transaction.** If you have 1.2 BTC in your wallet and you pay out 0.3, you have 0.9 BTC left, right? Well, yes. But it isn’t necessarily that simple. After all, you can have $100 in your physical wallet. That $100 could comprise two fifties...