Nuxeo Studio provides a list of registries that you can complete with JSON instructions.
The goal of this section of Studio is to be able to complete Nuxeo Studio drop down lists and elements of the interface with additional elements that come from another Studio project or an Eclipse-based customization. For example, you can declare a document type in the registries. You can then declare new document types from that type, use it in Structure Templates, etc. You can also use registries to declare new operations so that they appear in the Operations browser.
Examples are provided for each registry type.
For that reason, you can for instance only complete the "id" of a schema without the property detail, and you'll be able to assign this schema to a document type. But in that case you won't have the properties listed when editing some layouts on documents that hold this schema. You'll need to give the complete JSON definition for this.