Introducing bundle classes
Drupal.org change record, Oct 24, 2021
https://www.drupal.org/node/3191609
Drupal 9: Entity Bundle Classes
#! code, Jan 2, 2022
https://www.hashbangcode.com/article/drupal-9-entity-bundle-classes
Adding Bundle Subclasses to Drupal Core 9.3.0 (Part 1)
Derek Wright, TEN7, Jan 24, 2022
https://ten7.com/blog/post/adding-bundle-subclasses-drupal-core-930-part-1
Adding Bundle Subclasses to Drupal Core 9.3.0 (Part 2)
Derek Wright, TEN7, Jan 25, 2022
https://ten7.com/blog/post/adding-bundle-subclasses-drupal-core-930-part-2
Adding Bundle Subclasses to Drupal Core 9.3.0 (Part 3)
Derek Wright, TEN7, Jan 25, 2022
https://ten7.com/blog/post/adding-bundle-subclasses-drupal-core-930-part-3
Defining bundle fields in code
Joachim Noreiko, Joachim’s blog, Jan 31, 2022
http://www.noreiko.com/blog/defining-bundle-fields-code