<?php   if(isset($_POST['email'])){       $email = $_POST['email'];       if(filter_var($email, FILTER_VALIDATE_EMAIL)){           echo '<p>This is a valid email.<p>';       }else{           echo '<p>This is an invalid email.</p>';       }   }   ?>   <form action="" method="post">      Email: <input type="text" name="email" value=" <?php echo $_POST['email']; ?> ">      <input type="submit" value="Check Email">  </form>