اضافة ما بداخل حقل التكست بين كلام معين

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head>
  <title>some text</title>
<script type='text/javascript' src="jquery-1.4.4.js"></script>
 </head>





<body>
 <script type="text/javascript">
 $(function(){
    $('#button_submit').click(function(){
        $("#heretext").text($('#text_n').val());
    })
});

</script>

Text <input id="text_n"/>
<button type="button" id="button_submit">Submit</button>
some text <span id='heretext'>some text </span> some text
</body>

</html>