using php in collapsible-setn doesn't work

using php in collapsible-setn doesn't work

Is there a specific reason that I can't execute some basic php-code inside a collapsible-set?

I have tried it on many ways, but without succes. Is there some kind of basic rule which I don't know of?

My code is:

DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>jQuery Mobile-webtoepassing</title>




<link href="jquery.mobile-1.3.0.min.css" rel="stylesheet" type="text/css"/>
<link rel="stylesheet" type="text/css" href="style.css">


<script src="jquery-1.8.3.min.js" type="text/javascript"></script>
<script src="jquery.mobile-1.3.0.min.js" type="text/javascript"></script>

</head>
<body>


<?php
$verbinding=mysqli_connect("localhost","user","password","database");

if (mysqli_connect_errno($verbinding))
{
//echo "Verbinden is niet gelukt: " . mysqli_connect_error();
}
else
{
echo "Verbinden is gelukt!";
}?>






<section id="firstpage" data-role="page">
        <header data-role="header" data-theme="c" class="top">
            <h1>Jullie reacties</h1>
        </header>
 <div class="content" data-role="content">
 
 <div data-role="collapsible-set">
                <div data-role="collapsible">
               
<?php
$result = mysqli_query($verbinding,"SELECT * FROM comments
WHERE location_id=1");










while($row = mysqli_fetch_array($result))
  {
  echo $row['comment'] ;
  echo "<br>";
  }?>
 
</div>
<div data-role="collapsible">
 
<?php
echo "<h1>Twitter</h1>";
$result = mysqli_query($verbinding,"SELECT * FROM comments
WHERE location_id=2");











while($row = mysqli_fetch_array($result))
  {
  echo $row['comment'] ;
  echo "<br>";
  }
mysqli_close($verbinding);
?>
</div>
</div>
</div>








 <div data-role="footer"data-theme="c" class="foot">
  <h4>Sociale Media Ouderavond</h4>
 </div>
</section>


 Hope someone can tell me what I'm doing wrong.