~ Rot13 Encoder ~

<!DOCTYPE html>
<html>
<head><title>~ Rot 13 Encoder ~</title></head>
<body>
<center>
<h1 style="font-family: Monospace;">~ AnonGuy's Rot13 Encoder ~</h1>
<form method="post">
<textarea name="rawText" style="width: 369px; height: 257px;"></textarea><br><br><input style="width:37px;" type="submit" name="submit" value=">>" />
</form>
<?php
$postData = $_POST['rawText'];
$submit = $_POST['submit'];
function r0t($userInput) {return strtr($userInput, 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm');}
if   (isset($postData, $submit) && $submit == '>>'){
if   (ctype_alnum(str_replace(' ', '', $postData))) {echo '<h2 style="font-family: Monospace;">Output ~ </h2><code>'.r0t($postData).'</code><br><br>';}
else {echo '<p>Please Input Alphanumeric Values Only!</p>';}}
?>
</center></body></html>