var isNN = (navigator.appName.indexOf("Netscape")!=-1);

function autoTab(input, len, e) {
	var keyCode = (isNN) ? e.which : e.keyCode; 
	var filter = (isNN) ? [0,8,9,16] : [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;
}