Simplest possible text edit/modify

HTML

<h3>Editable DIV:</h3>
<div id="edit" contenteditable>Insert some linebreaks here.
</div>
<h3>Output:</h3>
<textarea>This will show the HTML of the DIV above.</textarea>

CSS

[contenteditable], textarea { border: double #ccc 3px; width: 500px; height: 200px; white-space:pre;}

JavaScript

$(document).ready(function(){
    $("#edit").on("keyup", function(){
       $("textarea").html($(this).html());
    });
});