Here is a description of the registry, from its Website:
This archive contains structured descriptions of legal resources and the publications from which they can be obtained. To view the descriptions for a given resource and jurisdiction, follow the links below.
The Registry is extensible: any visitor with a GitHub account can propose the addition of institutions, reporting services, or entire national jurisdictions. Proposals must be accepted by the editors of the Registry, and may be modified following discussion. To propose an addition or amendment, click on the link for a given resource in any Registry page, and follow the instructions provided in the source-code view. […]
About the metadata schemata used in the registry, Frank said:
The court IDs are an extension of the MLZ jurisdiction values, to court level. Metadata fields reflect citation practice.
For more details, please see the registry.
For updates on this post, please see the comments to this post.