the (poignant) guide to ruby is just great: "A range is two values surrounded by parentheses and separated by an ellipsis (in the form of two or three dots). Think of it as an accordion which has been squeezed down for carrying. (Sure, you can build a great sense of self-worth by carrying around an unfolded accordion, but sometimes a person needs to wallow in self-doubt, carefully concealing the squeeze-box.) The parentheses are the handles on the sides of a smaller, handheld accordion. The dots are the chain, keeping the folds tightly closed. Normally, only two dots are used. If a third dot is used, the last value in the range is excluded. When you see that third dot, imagine opening the accordion slightly. Just enough to let one note from its chamber. The note is that end value. WeBAD+92ll let the sky eat it."