code: function(s1, s2, v, d) { 
  				var s = {}, val, p;
  				for (p in s2) {
  					if (p !== "cssText") if (p !== "length") if (isNaN(p)) if (s1[p] != (val = s2[p])) if (val !== _transformProp) if (typeof(val) === "number" || typeof(val) === "string") {
  						s[p] = ((val === "" || val === "auto") && typeof(s1[p]) === "string" && s1[p].replace(_NaNExp, "") !== "") ? 0 : val; //if the ending value is defaulting ("" or "auto"), we check the starting value and if it can be parsed into a number (a string which could have a suffix too, like 700px), then we swap in 0 for "" or "auto" so that things actually tween.
  						if (d) {
  							d.props.push(p);
  						}
  					}
  				}
  				if (v) {
  					for (p in v) { //copy properties (except className)
  						if (p !== "className") {
  							s[p] = v[p];
  						}
  					}
  				}
  				return s;
  			}
docs: set up some local variables and functions that we can reuse for all tweens - we do this only once and cache things to improve performance