enter a tab key in editable div
function onKeyDown(e) {
if (e.keyCode === 9) { // tab key
e.preventDefault(); // this will prevent us from tabbing out of the editor
// now insert four non-breaking spaces for the tab key
var editor = document.getElementById("editor");
var doc = editor.ownerDocument.defaultView;
var sel = doc.getSelection();
var range = sel.getRangeAt(0);
var tabNode = document.createTextNode("\u00a0\u00a0\u00a0\u00a0");
range.insertNode(tabNode);
range.setStartAfter(tabNode);
range.setEndAfter(tabNode);
sel.removeAllRanges();
sel.addRange(range);
}
}