读不懂这个for循环里的内容啊,谁能逐条注释
for(var i = 0; i < allli.length; i++) {
allli[i].index = i;
allli[i].onmouseover = function() {
for(var i = 0; i < allli.length; i++) {
allli[i].className = "#ul1 li";
}
this.className = "liactive";
for(var j = 0; j <alltittle.length; j++) {
alltittle[j].className = "title hidden";
}
alltittle[this.index].className = "title active";
}
}