This is a continuation of a previous post. If you haven't read it I suggest that you do so before reading further, otherwise you won't understand the context.
This is the first part in a series of posts that I have written on this topic. In this first post I will discuss the reasons why I ported the module to Drupal 8 and some of the more basic module code (YAML files and forms). In the next post I will go over the Plugin system, how to write a custom Plugin, and how to implement the Batch API.
I was recently given a requirement by a client in which they wanted content authors to be able to find and replace instances of words across potentially every piece of content in the site. This is a request that I've received in the past and have been able to solve the problem with relative ease. In Drupal 7 (D7) there is a module called scanner, which does exactly what they needed.