code: function(ratio) {
  			var target = this.target,
  				a = this.a,
  				i = a.length,
  				e, val;
  			if (this._round) {
  				while (--i > -1) {
  					e = a[i];
  					target[e.i] = Math.round(e.s + e.c * ratio);
  				}
  			} else {
  				while (--i > -1) {
  					e = a[i];
  					val = e.s + e.c * ratio;
  					target[e.i] = (val < 0.000001 && val > -0.000001) ? 0 : val;
  				}
  			}
  		}
docs: called each time the values should be updated, and the ratio gets passed as the only parameter (typically it's a value between 0 and 1, but it can exceed those when using an ease like Elastic.easeOut or Back.easeOut, etc.)