Unnamed

<? $message = ""; if(isset($_POST["submit"]) && !isset($_POST["checkbox"])) { $message = "Check the box."; } else { header("location:nextpage.php"); } ?><html><head><body><form action="thispage.php" method="post"> <?=$message ?>  <input type="checkbox" name="checkbox"> You must check this. <input type="submit" name="submit"></form></body>