Checkbox POST

Code

<?php
error_reporting(E_ALL);

$checked = isSet($_POST["checkbox"]);
?>
<!DOCTYPE html>
<html>
        <head>
                <title>Checkbox POST</title>
        <head>
        <body>
                <h1>Checkbox POST</h1>

                <?php
                if (strToLower($_SERVER["REQUEST_METHOD"]) === "post")
                {
                ?>
                        <p>The checkbox is <b><?php echo ($checked) ? "checked" : "not checked"; ?></b>.</p>
                <?php
                }
                ?>

                <form method="post">
                        <p><input type="checkbox" name="checkbox" value="checked"></p>
                        <p><input type="submit" value="Check"></p>
                </form>

                <h2>Code</h2>

                <?php echo highlight_file(__FILE__, true); ?>

                <p><small>(Example made for <a href="http://gathering.tweakers.net/forum/list_messages/1431893">this topic</a> on <a href="http://gathering.tweakers.net/forum/">GoT</a>.)</small></p>
        </body>
</html>

(Example made for this topic on GoT.)