//USAGE: <input type="text" name="nxx" maxlength="3" size="6" value="" onkeyup="return autoTab(this, 3, event)"/>

var isNN = (navigator.appName.indexOf("Netscape")!=-1);
if(isNN)
        document.captureEvents(Event.KEYPRESS);
function autoTab(input,len, e){
        var keyCode = (isNN)?e.which:e.keyCode;
        var filter = (isNN)?[0,8,9]:[0,8,9,16,17,18,37,38,39,40,46];
        if(input.value.length >= len && !containsElement(filter,keyCode)){
        input.value = input.value.slice(0,len);
        input.form[(getIndex(input)+1)%input.form.length].focus();
}
        
function containsElement(arr, ele){
        var found = false, index = 0;
    while(!found && index < arr.length)
        if(arr[index]==ele)
                found = true;
        else
                index++;
    return found;
}
  
function getIndex(input){
        var index = -1, i = 0, found = false;
    while (i < input.form.length && index==-1)
        if (input.form[i] == input)index = i;
        else i++;
    return index;
        }
  return true;
}
//  End -->