page.html.twig default regions I'm creating a custom theme with base theme: stable. I have copied the template/layout/page.html.twig file into my theme. As I am reading the twig file I have noticed that there are some regions that I am not providing but are still being rendered.

Part of the file comment lists the regions available.

/*
 * Regions:
 * - page.header: Items for the header region.
 * - page.primary_menu: Items for the primary menu region.
 * - page.secondary_menu: Items for the secondary menu region.
 * - page.highlighted: Items for the highlighted content region.
 * - page.help: Dynamic help text, mostly for admin pages.
 * - page.content: The main content of the current page.
 * - page.sidebar_first: Items for the first sidebar.
 * - page.sidebar_second: Items for the second sidebar.
 * - page.footer: Items for the footer region.
 * - page.breadcrumb: Items for the breadcrumb region.
 */


I went looking in the stable.info.yml file and noticed there is not an entry for regions: so I am at a loss as how the page.html.twig file is able to render regions that are not listed in the stable.info.yml file.

Questions


How does this work without being defined in the stable.info.yml file.
Are there any other regions that work like this that are not in the page.html.twig file.
If no regions are specified in the theme, the core provides defaults itself.

From the docs page: https://www.drupal.org/docs/8/theming-drupal-8/adding-regions-to-a-theme


  Default Regions:
  
  page.header: Items for the header region.
  
  page.primary_menu: Items for the primary menu region.
  
  page.secondary_menu: Items for the secondary menu region.
  
  page.highlighted: Items for the highlighted content region.
  
  page.help: Dynamic help text, mostly for admin pages.
  
  page.content: The main content of the current page.
  
  page.sidebar_first: Items for the first sidebar.
  
  page.sidebar_second: Items for the second sidebar.
  
  page.footer: Items for the footer region.
  
  page.breadcrumb: Items for the breadcrumb region.
  
  If your theme does not declare any regions Drupal will assume this set
  of defaults. These regions correspond with what the default
  core/modules/system/templates/page.html.twig file expects, as well as
  two hidden regions, page_top, and page_bottom - you don't need to
  declare these final two if you override the defaults, however the {{
  page_top }} and {{ page_bottom }} Twig variables should be retained
  in the html.html.twig template.