Why is the output of the passed value of the variable in the browser window?

Question

PHP

Server: Microsoft-IIS/7.5 /PHP5.5.30
If the id is deleted directly in the browser line, then there will be nothing on the ID value screen, only the content part will remain (as intended)...

File connection using id

echo $id;
    switch($id){
      case 'home':
        include 'home.php';break;
      case 'testing':
        include 'testing.php';break;
      case 'plans':
        include 'plans.php';break;
      default:
        include 'index.inc.php';
    }
    ?>

Content area content:

<h2> Раздел находится в разработке </h2>
<p> На данной сранице Вы сможете проверить свои знания </p>

Answer 1

echo $id; //ни на что не намекает?