Signatures object is not defined explicitly

I'm not quite sure how to organize this, but I think that the Signatures object could use a little more definition.

The Signatures object is referred to several times in the Federation API, but it isn't explicitly defined like other objects types are. There is a reference to the Signing JSON (section 3) in the appendix, but the actual schema isn't described until Section 3.2. It requires some scrolling to get down to the definition from the link given in the Federation API.

A sentence in Section 3.2 of the appendix mentions that the key for the field is "the name of the entity signing it." For device signatures, it is explicitly stated that the entity name is the User ID and the signing key identifier is the concatenation of the algorithm and device ID. (Cf. signatures request parameter in key claim endpoint.

On the other hand, for server signatures it doesn't seem to be explicitly stated that the key for a homeserver signature should be the server name. This can be inferred from the examples, but it could be made more explicit. I think it would be nice to have a type defined for Signatures something like this:

Signatures (generic)

This could be further specified for each signature type:

Server Signatures

Device Signatures

... and similarly for the Invite Signatures and Identity Server Signatures types.

(Now that I write this, it seems that the difficulty with this is being able to specify types for field names...)

Sorry for the rambling; let me know if I didn't get the problem across.

Comienza con las referencias de la Federation API al objeto Signatures, después lee el apéndice de Signing JSON, especialmente la Sección 3.2, y compara los ejemplos de firmas de device y server. Aclara el mapeo genérico de nombres de entidad y documenta las variantes server, device, invite e identity-server. Se considera terminado cuando las secciones de la API referenciadas definen los nombres de las claves y los mapas de valores sin requerir que los lectores los infieran a partir de los ejemplos.