API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...
On this page #route_parameters attribute in missing on properties list. It's important to know about this if you need to use a route name that has mandatory parameters.
This attribute is documented and used in pager preprocess function:
https://api.drupal.org/api/drupal/core!includes!theme.inc/function/templ...