Entity initializers create entities and initialize the entity's data from an Action Context. This system is not final and will likely change in the future, especially with data components on the way. Very few of them have actual fields, and some of them are specialized, such as projectiles copying the item stack or minecarts checking whether the target position is valid or not. The entity initializer type is the same as the entity type and is determined by the type field. All types with actual fields are found in the sidebar.