es we explained different aspects of the syntax used by the Migrate API. In today’s article, we are going to dive deeper to understand how the API interprets our migration definition files. We will explain how to configure process plugins and set subfields and deltas for multi-value field migrations. We will also talk about process plugin chains, source constants, pseudofields, and the process pipeline. After reading this article, you will better comprehend existing migration definition files and improve your own. Let’s get started.