I realized the answer as I was posting my own question: This is the most succinct way of taking the min of an array x in JavaScript. The first argument is totally arbitrary; I find the 0 confusing because the code intuitively means “Take the min of 0 and x,” which is absolutely not the case. Using the Math object makes more sense for human-readability, but the Raphael.js authors are obsessed with minification and 0 is three bytes shorter.
See http://ejohn.org/blog/fast-javascript-maxmin/
For readability’s sake, I’d strongly urge people to stop doing this and instead define a function along the lines of
function arrayMin(arr) { return Math.min.apply(Math, arr); };