It works with Array types. The example is a simple list of numbers, but the array could contain anything; lists of strings, functions, DOM nodes, whatever. Unfortunately, a lot of things that seem like arrays in the DOM aren't really, so you can't shuffle the images on a page with just document.images.shuffle() all by itself.

Very useful function that you can use to debug/show your array and it's contents.

Sometimes when you have problems with arrays and print_r() isn't very nice way to show array values because it shows everything in one line and then it is very hard to debug... this way I think it's much much easier.