Previously named RegistryKeyAttachment before deobfuscation, Resource Key Attachments (RKAs) are a way to associate objects present in a Registry (not a lite one) by associating their resource keys.

Their concept is highly inspired from the old RegsitryEntryAttachment (REAs) system from the old Quilt Standard Libraries. The main difference is that RKAs works with the object keys, while REAs worked with just the objects.

There are two types of them, for the two sorts of Registries you can encounter in Minecraft's codebase:

• ResourceKeyAttachment, made for Standard/Builtin Registries.
• DynamicResourceKeyAttachment, made for Dynamic Registries.

ResourceKeyAttachment

You can create a simple RKA with RegistryKeyAttachment#create(Registry). Just provide the registry object for the RKA; vanilla ones can be found in the BuiltinRegistries class.

You'll then have three methods, put, contains and get, and every of them either takes the object to collect the attachment from, or the resource key of the object directly.

DynamicResourceKeyAttachment

For those, you can create them with DynamicRegistryKeyAttachment#create(ResourceKey). The key it is asking for is the registry's resource key; vanilla ones can be found in the Registries class.

You'll then have the same three methods name than the simple RKA, but, there's a thing; to put/check presence/get the attachments from the object, you must also provide a RegistryAccess. For example, if you have access to a Level object, you can find the RegistryAccess in Level#registryAcces.