help me to understand this nasty code ... put some comments...

<script type='text/javascript'>
// <![CDATA[
var colour="#38ACEC"; //colour code
var sparkles=40;

var x=ox=400;
var y=oy=300;
var swide=800;
var shigh=600;
var sleft=sdown=0;

var tiny=new Array();
var star=new Array();
var starv=new Array();
var starx=new Array();
var stary=new Array();
var tinyx=new Array();
var tinyy=new Array();
var tinyv=new Array();
window.onload=function()
{
if (document.getElementById)
{
var i, rats, rlef, rdow; // variables used to create L
for (var i=0; i<sparkles; i++) // to display the L
{
var rats=createDiv(3,3); // height and width is passed of 'rectangle' through function createDiv
rats.style.visibility="hidden"; //rectangle created is hidden
document.body.appendChild(tiny[i]=rats); //append child 'L' to the document's body & each loop time 39 'L'are created
starv[i]=0;
tinyv[i]=0;
var rats=createDiv(5,5); // later on size increased of 'rectangle'
rats.style.backgroundColor="transparent";

rats.style.visibility="hidden";

var rlef=createDiv(1, 5);
var rdow=createDiv(5, 1);
rats.appendChild(rlef);
rats.appendChild(rdow);
rlef.style.top="3px";
rlef.style.left="0px";
rdow.style.top="0px";
rdow.style.left="3px";
document.body.appendChild(star[i]=rats);
}
set_width();
sparkle();
}}
function sparkle() {
var c;
if (x!=ox || y!=oy) {
ox=x;
oy=y;
for (c=0; c<sparkles; c++) if (!starv[c]) {
star[c].style.left=(starx[c]=x)+"px";

star[c].style.top=(stary[c]=y)+"px";
star[c].style.clip="rect(0px, 5px, 5px, 0px)";
star[c].style.visibility="visible";
starv[c]=50;
break;
}
}
for (c=0; c<sparkles; c++) {
if (starv[c]) updatestar(c);
if (tinyv[c]) updatetiny(c);
}
setTimeout("sparkle()", 40);
}
function update_star(i) {
if (--starv[i]==25) star[i].style.clip="rect(1px, 4px, 4px, 1px)";
if (starv[i]) {
stary[i]+=1+Math.random()*3;
if (stary[i]<shigh+sdown) {
star[i].style.top=stary[i]+"px";
starx[i]+=(i%5-2)/5;
star[i].style.left=starx[i]+"px";
}
else {
star[i].style.visibility="hidden";
starv[i]=0;
return;
}

}
else {
tinyv[i]=50;
tiny[i].style.top=(tinyy[i]=stary[i])+"px";
tiny[i].style.left=(tinyx[i]=starx[i])+"px";
tiny[i].style.width="2px";
tiny[i].style.height="2px";
star[i].style.visibility="hidden";
tiny[i].style.visibility="visible"
}
}
function update_tiny(i) {
if (--tinyv[i]==25) {
tiny[i].style.width="1px";
tiny[i].style.height="1px";
}
if (tinyv[i]) {
tinyy[i]+=1+Math.random()*3;
if (tinyy[i]<shigh+sdown) {
tiny[i].style.top=tinyy[i]+"px";
tinyx[i]+=(i%5-2)/5;
tiny[i].style.left=tinyx[i]+"px";
}
else {

tiny[i].style.visibility="hidden";
tinyv[i]=0;
return;
}
}
else tiny[i].style.visibility="hidden";
}
document.onmousemove=mouse;
function mouse(e) {
setscroll();
y=(e)?e.pageY:event.y+sdown;
x=(e)?e.pageX:event.x+sleft;
}
function setscroll() {
if (typeof(self.pageYOffset)=="number") {
sdown=self.pageYOffset;
sleft=self.pageXOffset;
}
else if (document.body.scrollTop || document.body.scrollLeft) {
sdown=document.body.scrollTop;
sleft=document.body.scrollLeft;
}
else if (document.documentElement && (document.documentElement.scrollTop || document.documentElement.scrollLeft)) {
sleft=document.documentElement.scrollLeft;
sdown=document.documentElement.scrollTop;
}
else {
sdown=0;
sleft=0;
}
}
window.onresize=setwidth;
function setwidth() {
if (typeof(self.innerWidth)=="number") {
swide=self.innerWidth;
shigh=self.innerHeight;
}
else if (document.documentElement && document.documentElement.clientWidth) {
swide=document.documentElement.clientWidth;
shigh=document.documentElement.clientHeight;
}
else if (document.body.clientWidth) {
swide=document.body.clientWidth;
shigh=document.body.clientHeight;
}
}
function createDiv(height, width) {
var div=document.createElement("div"); // creating an element div
div.style.position="absolute"; // setting position of sparkle
div.style.height=height+"px"; // paramter height
div.style.width=width+"px"; // paramter width
div.style.overflow="hidden"; //what happens if content overflows
div.style.backgroundColor=colour; //assigned to variable colour
return (div); //returning div element
}
// ]]>
</script>
<body>

<div id="coordiv"
onmousemove="createDiv(height, width)"></div>

cursor style</p>

</body>
</html>