text: // http://paulirish.com/2011/requestanimationframe-for-smart-animating/
  // http://my.opera.com/emoller/blog/2011/12/20/requestanimationframe-for-smart-er-animating
  
  // requestAnimationFrame polyfill by Erik Möller
  // fixes from Paul Irish and Tino Zijdel
  
  (function() {
  	var lastTime = 0;
  	var vendors = ['ms', 'moz', 'webkit', 'o'];
  	for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
  		window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
  		window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] || window[vendors[x] + 'CancelRequestAnimationFrame'];
  	}
  
  	if (!window.requestAnimationFrame)
  		window.requestAnimationFrame = function(callback, element) {
  			var currTime = new Date().getTime();
  			var timeToCall = Math.max(0, 16 - (currTime - lastTime));
  			var id = window.setTimeout(function() {
  					callback(currTime + timeToCall);
  				},
  				timeToCall);
  			lastTime = currTime + timeToCall;
  			return id;
  		};
  
  	if (!window.cancelAnimationFrame)
  		window.cancelAnimationFrame = function(id) {
  			clearTimeout(id);
  		};
  }());