Adding support for _defaults key to the your_module.services.yml file

Drupal adds the functionality to set default values for all your services in the your_module.services.yml file. 3 keys can be set: autowire, public and tags. All declared services will get those set values from _defaults as default values in their service definition.

Drupal is adding the functionality from the Symfony project. See https://symfony.com/doc/current/service_container.html

Example for your_module.services.yml:

services:
  _defaults:
    autowire: true
    public: true
    tags:
      - 'foo.tag'
      - {name: bar.tag, value: 123}
  your_service:
    class: Drupal\your_module\YourClass