为什么php标签没有在drupal中关闭？

这是index.PHP中的代码,只有<？PHP,但没有？>,这是我第一次看到这样的代码,有什么原因吗？

<?PHP
// $Id: index.PHP,v 1.94 2007/12/26 08:46:48 dries Exp $

/**
 * @file
 * The PHP page that serves all page requests on a Drupal installation.
 *
 * The routines here dispatch control to the appropriate handler,which then
 * prints the appropriate page.
 *
 * All Drupal code is released under the GNU General Public License.
 * See copYRIGHT.txt and LICENSE.txt.
 */

require_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

$return = menu_execute_active_handler();

// Menu status constants are integers; page content is a string.
if (is_int($return)) {
  switch ($return) {
    case MENU_NOT_FOUND:
      drupal_not_found();
      break;
    case MENU_ACCESS_DENIED:
      drupal_access_denied();
      break;
    case MENU_SITE_OFFLINE:
      drupal_site_offline();
      break;
  }
}
elseif (isset($return)) {
  // Print any value (including an empty string) except NULL or undefined:
  print theme('page',$return);
}

drupal_page_footer();

省略结束标记可防止意外将尾随空白空间注入响应中.

在某些框架中是常见的编码实践,如Zend.