index.php:

require_once './includes/bootstrap.inc';
// pääsee tänne

drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
// ei pääse tänne

// bootstrap.inc:

function drupal_bootstrap($phase = NULL) {
  static $phases = array(DRUPAL_BOOTSTRAP_CONFIGURATION, DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE, DRUPAL_BOOTSTRAP_DATABASE, DRUPAL_BOOTSTRAP_ACCESS, DRUPAL_BOOTSTRAP_SESSIO$

  if (isset($phase)) {
    while ($phase >= $phase_index && isset($phases[$phase_index])) {
      $current_phase = $phases[$phase_index];
      unset($phases[$phase_index++]);
      _drupal_bootstrap($current_phase);
    }
  }
    // pääsee tänne
        return $phase_index;
}