页面搜索是怎么做了?http://www.ylstudy.net/article/article.asp

Question

着是一个JS文件，有页面搜索函数。自己看看吧
var NS4 = (document.layers);
var IE4 = (document.all);var win = this;
var n   = 0;function findInPage(str)
{
var txt, i, found;
if (str == "")
return false;
if (NS4)
{
if (!win.find(str))
while(win.find(str, false, true))
n++;
else
n++;
if (n == 0) alert(str + " ...您要找的答案不存在。请试着输入该题目中的关键字再次查找！并且请注意，不要把“？”或“：”也输入查找！！！");
} if (IE4)
{
txt = win.document.body.createTextRange();
for (i = 0; i <= n && (found = txt.findText(str)) != false; i++)
{
txt.moveStart("character", 1);
txt.moveEnd("textedit");
}
if (found)
{
 txt.moveStart("character", -1);
 txt.findText(str);
 txt.select();
 txt.scrollIntoView();
 n++; }
else
{
if (n > 0)
{
n = 0;
findInPage(str);
}
else
alert(str + "...您要找的答案不存在。请试着输入该题目中的关键字再次查找！并且请注意，不要把“？”或“：”也输入查找！！！");
}
}
return false;
}self.onError=null;
currentX = currentY = 0;  
whichIt = null;   
         lastScrollX = 0; lastScrollY = 0;
NS = (document.layers) ? 1 : 0;
IE = (document.all) ? 1: 0;
<!-- STALKER CODE -->
function heartBeat() {
if(IE) { diffY = document.body.scrollTop; diffX = document.body.scrollLeft; }
    if(NS) { diffY = self.pageYOffset; diffX = self.pageXOffset; }
if(diffY != lastScrollY) {                 percent = .1 * (diffY - lastScrollY);
                if(percent > 0) percent = Math.ceil(percent);
                else percent = Math.floor(percent); if(IE) document.all.floater.style.pixelTop += percent;
if(NS) document.floater.top += percent;                  lastScrollY = lastScrollY + percent;
    }
if(diffX != lastScrollX) {
percent = .1 * (diffX - lastScrollX);
if(percent > 0) percent = Math.ceil(percent);
else percent = Math.floor(percent);
if(IE) document.all.floater.style.pixelLeft += percent;
if(NS) document.floater.left += percent;
lastScrollX = lastScrollX + percent;
}
} <!-- /STALKER CODE -->
<!-- DRAG DROP CODE -->
function checkFocus(x,y) { 
        stalkerx = document.floater.pageX;
        stalkery = document.floater.pageY;
        stalkerwidth = document.floater.clip.width;
        stalkerheight = document.floater.clip.height;
        if( (x > stalkerx && x < (stalkerx+stalkerwidth)) && (y > stalkery && y < (stalkery+stalkerheight))) return true;
        else return false;
} function grabIt(e) {
if(IE) {
whichIt = event.srcElement;
while (whichIt.id.indexOf("floater") == -1) {
whichIt = whichIt.parentElement;
if (whichIt == null) { return true; }
    }
whichIt.style.pixelLeft = whichIt.offsetLeft;
    whichIt.style.pixelTop = whichIt.offsetTop;
currentX = (event.clientX + document.body.scrollLeft);
    currentY = (event.clientY + document.body.scrollTop); 
} else { 
        window.captureEvents(Event.MOUSEMOVE);
        if(checkFocus (e.pageX,e.pageY)) { 
                whichIt = document.floater;
                StalkerTouchedX = e.pageX-document.floater.pageX;
                StalkerTouchedY = e.pageY-document.floater.pageY;
        }  }
    return true;
}
function moveIt(e) {
if (whichIt == null) { return false; }
if(IE) {
    newX = (event.clientX + document.body.scrollLeft);
    newY = (event.clientY + document.body.scrollTop);
    distanceX = (newX - currentX);    distanceY = (newY - currentY);     currentX = newX;    currentY = newY;
    whichIt.style.pixelLeft += distanceX;     whichIt.style.pixelTop += distanceY;
if(whichIt.style.pixelTop < document.body.scrollTop) whichIt.style.pixelTop = document.body.scrollTop; if(whichIt.style.pixelLeft < document.body.scrollLeft) whichIt.style.pixelLeft = document.body.scrollLeft;
if(whichIt.style.pixelLeft > document.body.offsetWidth - document.body.scrollLeft - whichIt.style.pixelWidth - 20) whichIt.style.pixelLeft = document.body.offsetWidth - whichIt.style.pixelWidth - 20;
if(whichIt.style.pixelTop > document.body.offsetHeight + document.body.scrollTop - whichIt.style.pixelHeight - 5) whichIt.style.pixelTop = document.body.offsetHeight + document.body.scrollTop - whichIt.style.pixelHeight - 5;
event.returnValue = false;
} else {
whichIt.moveTo(e.pageX-StalkerTouchedX,e.pageY-StalkerTouchedY);
        if(whichIt.left < 0+self.pageXOffset) whichIt.left = 0+self.pageXOffset;
        if(whichIt.top < 0+self.pageYOffset) whichIt.top = 0+self.pageYOffset;
        if( (whichIt.left + whichIt.clip.width) >= (window.innerWidth+self.pageXOffset-17)) whichIt.left = ((window.innerWidth+self.pageXOffset)-whichIt.clip.width)-17;
        if( (whichIt.top + whichIt.clip.height) >= (window.innerHeight+self.pageYOffset-17)) whichIt.top = ((window.innerHeight+self.pageYOffset)-whichIt.clip.height)-17;
        return false;
}
    return false;
}
function dropIt() {
whichIt = null;
    if(NS) window.releaseEvents (Event.MOUSEMOVE);
    return true;
}
<!-- DRAG DROP CODE -->
if(NS) {
window.captureEvents(Event.MOUSEUP|Event.MOUSEDOWN);
window.onmousedown = grabIt;
  window.onmousemove = moveIt;
window.onmouseup = dropIt;
}
if(IE) {
document.onmousedown = grabIt;
  document.onmousemove = moveIt;
document.onmouseup = dropIt;
}
if(NS || IE) action = window.setInterval("heartBeat()",1);document.write('<div ID="floater" align="center"></tr><tr><td width="100%" class="ourfont"><table border="1" width="100%" cellspacing="0" cellpadding="0" bgcolor="#008000" bordercolorlight="#008000" bordercolordark="#FFFFFF"><tr><td width="100%" bgcolor="#D9D9FF" valign="middle" align="center"><form name="search1" onSubmit="return findInPage(this.string1.value);"><p><font color="#FF0000" class="ourfont">查询本页：</font><input alt="查询" border="0" src="find.gif" type="image" name="搜索" WIDTH="50" HEIGHT="27"><br><input name="string1" type="text" size="40" onChange="n = 0;" ');
document.write("onFocus=window.document.search1.string1.value=''  class='ourfont'><form></td></tr><tr><td width='100%' bgcolor='#D9D9FF' valign='middle' align='center'><span class='ourfont'><font color='#400040'>可以用鼠标拖动此窗口！</font></span></td></tr></table></td></tr></table></div></form>");