Escaped html in 'please login to chat' dialog

The following code:

356 else if ($user->uid == 0) {
357 $output .= t('Please %login to chat', array('%login' => l('login', 'user/login')));
358 }

prints the HTML substituded by l(login, 'user/login') as filtered through check_plain. Thus, the html appears inline.

If you instead use !login, it will not run the html through check plain using the default theme_placeholder function:
http://api.drupal.org/api/function/theme_placeholder/5