关于onmouseover,onmouseout,onclick这三个事件的问题【在线等】

<BODY>
<style>
body,td { font-size:9pt; font-family:tahoma; text-align:center; }
.over { background-color:#006600; color:#ffffff; cursor:default; }
.click { background-color:#CC0033; color:#ffffff; cursor:default; }
.out { background-color:#ffffff; cursor:default; }
</style>
<TABLE border=1 id=t width=500 height=200>
<TR>
<TD onmouseover="HandleOver(this)" onclick="HandleClick(this)" onmouseout="HandleOut(this)">never</TD>
<TD onmouseover="HandleOver(this)" onclick="HandleClick(this)" onmouseout="HandleOut(this)">Html</TD>
<TD onmouseover="HandleOver(this)" onclick="HandleClick(this)" onmouseout="HandleOut(this)">editor</TD>
</TR>
</TABLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
function HandleClick(obj) {
for(var i=0;i<t.rows.length;i++) {
for(var j=0;j<t.rows[i].cells.length;j++) {
if(t.rows[i].cells[j]!=obj)
t.rows[i].cells[j].className='out';
else
t.rows[i].cells[j].className='click';
}
}
}
function HandleOver(obj) {
if(obj.className=='click')return;
obj.className='over';
}
function HandleOut(obj) {
if(obj.className=='click')return;
obj.className='out';
}
//-->
</SCRIPT>
</BODY>