By resorting to YAML files for configuration, Drupal 8 achieved a huge boost in flexibility and understandability of the parameters. Even more it is useful for such a “commonly uncommon” task as migration.
Indeed, in D7 you had a set of forms to match source to destination, using some limited set of processing options. Now, in D8, these three stages of migration are totally separated out, unleashing a (nearly) unlimited power of building processing pipes and referencing other migrations. Continue reading