Custom Data Namespacing

Custom Data Component

Packs MUST NOT define any data in the minecraft:custom_data component outside of the path/struct <pack ID>. (I.e. all data defined in minecraft:custom_data must have it's path start with <pack ID>..)

As of Minecraft version 1.21.11, this applies to items, blocks, and entities. Entities have their minecraft:custom_data at path data, as opposed to components."minecraft:custom_data".

From Private:

Data at path <pack ID>._ in the minecraft:custom_data component [is defined as private].

Pack-Defined Data Locations

In instances where a pack defines it's own public shared data location with the intention of other packs storing/defining arbitrary data (i.e. serves a similar function of the minecraft:custom_data component), the same rules for minecraft:custom_data mentioned above SHOULD be enforced/followed. This includes the indication of private; data at relative path <pack ID>._ SHOULD be treated as private.