I am trying to pre-fill my form with data that is found in my .php file. Please, what am I doing wrong? The form field displays exactly what is found in between quotes.

```
<form  id='registration' method="POST" action="m.php" >
 Username:<br><input type="read-only" name="username" value="<?php echo htmlspecialchars($ss); ?>" /><br>

```

This is the .php file

```
<?php
session_start();
if($_SESSION["logged_in"] == true){
    $ss=$_SESSION['username'];
    }
else $ss="nu";
?>

```