Event dispatchers and Event subscribers for Drupal 8

I did a little exploration into Event dispatchers and Event subscribers for Drupal 8 and found some helpful articles which I am saving here for future reference:

• https://www.drupal.org/docs/8/creating-custom-modules/subscribe-to-and-d...
• https://www.chapterthree.com/blog/how-to-register-event-subscriber-drupal8
• http://www.drupal8.ovh/en/tutoriels/358/event-dispatcher-create-event-di...
• https://www.valuebound.com/resources/blog/how-to-define-an-event-dispatc...