<script type="text/javascript">
(function($){
	function getCaret(){
		var fullText=$('#elm1').html().replace(/<[^>]+>/g,''),
		selectedText=$('#elm1').tinymce().selection.getContent({format : 'text'}),
		start=fullText.indexOf(selectedText);
		return ""+start+","+(start+selectedText.length);
	}
	$("document").ready(function() {
		setTimeout(function(){
			$("body",$("iframe")[0].contentWindow.document).keyup(function(){
				$("#result").text(":"+getCaret());
			})
			.mousemove(function(){
				$("#result").text(":"+getCaret());
			})
			.mouseup(function(){
				$("#result").text(":"+getCaret());
			});
		},1000);
	});
})(jQuery);
</script>
<div>Caret Position <span id="result"></span></div>