Why does CodeIgniter output a piece of code?

Question

CodeIgniter

The code:

<?
defined('BASEPATH') OR exit('No direct script access allowed');

  /**
   *
   */
  class Notfound extends CI_Controller
  {

    private $page = '404';

    function __construct()
    {
      parent::__construct();
    }

    public function index()
    {
      $this->output->set_status_header('404');
      $data['page'] = $this->page;
      $this->load->view('header', $data);
      $this->load->view('404');
      $this->load->view('footer');
    }

  }

Conclusion: