这是多级关联菜单！但是我不明白这个代码？
谁能给我注释一下

function change(v){
    var str="0";
    for(i=0;i<v;i++){ str+=("_"+(document.getElementById(s[i]).selectedIndex-1));};
    var ss=document.getElementById(s[v]);
        with(ss){
        length = 0;
            options[0]=new Option(opt0[v],opt0[v]);
        if(v && document.getElementById(s[v-1]).selectedIndex>0 || !v)
        {
            if(dsy.Exists(str)){
                ar = dsy.Items[str];
                for(i=0;i<ar.length;i++)options[length]=new Option(ar[i],ar[i]);
                if(v)options[1].selected = true;
            }
        }
        if(++v<s.length){change(v);}