Explain the meaning of floating advertising code in Web pages

Web page floating wide picture special effects, this special effect we always like, the mouse points to picture after the picture stopped moving.

<pre>
<div id= "ad" style= "Position:absolute" ><a href= "http://www.cnwebshow.com"
< IMG src= "/img/200406301.jpg" border= "0" ></A>
</div>
<script>
var x = 50,y =%
var Xin = true, Yin = True
var step = 1
var delay = ten
var obj=document.getelementbyid ("ad")
function Floatad () {
var l=t=0
var r= document.body.clientwidth-obj.offsetwidth
var B = Document.body.clientheight-obj.offsetheight
Obj.style.left = x + document.body.scrollLeft
Obj.style.top = y + Document.body.scrollTop
x = x + step* (xin?1:-1)
if (x < l) {Xin = true; x = L}
if (x > R) {xin = false; x = R}
y = y + step* (yin?1:-1)
if (Y < T) {Yin = true; y = T}
if (Y > B) {yin = false; y = b}
}< Br>var itl= setinterval ("Floatad ()", delay)
Obj.onmouseover=function () {clearinterval (ITL)}
obj.onmouseout= function () {Itl=setinterval ("Floatad ()", delay)}
</script>
</pre>