Missing site related variables in page.tpl.php

The page.tpl.php documentation says that site related variables are available:

 * Site identity:
 * - front_page: The URL of the front page. Use this instead of base_path when
 *   linking to the front page. This includes the language domain or prefix.
 * - logo: The url of the logo image, as defined in theme settings.
 * - site_name: The name of the site. This is empty when displaying the site
 *   name has been disabled in the theme settings.
 * - site_slogan: The slogan of the site. This is empty when displaying the site
 *   slogan has been disabled in theme settings.

If you print these variables in page.html.twig it doesn't work. Site related variables now come from site branding block. So it makes more sense to remove from the documentation of page.html.twig.