Табуляция в textarea при нажатии кнопки Tab

function insertTab(evt, obj)
{
evt = evt || window.event;
var keyCode = evt.keyCode || evt.which || 0;

if(keyCode == 9)
{
if(document.selection)
{
document.selection.createRange().duplicate().text = "\t";
}
else if(obj.setSelectionRange)
{
var strFirst = obj.value.substr(0, obj.selectionStart);
var strLast  = obj.value.substr(obj.selectionEnd, obj.value.length);

obj.value = strFirst + "\t" + strLast;

var cursor = strFirst.length + "\t".length;

obj.selectionStart = obj.selectionEnd = cursor;
}

if(evt.preventDefault && evt.stopPropagation)
{
evt.preventDefault();
evt.stopPropagation();
}
else {
evt.returnValue = false;
evt.cancelBubble = true;
}

return false;
}
}

<textarea onkeydown="insertTab(event, this)">