It's not really clear to me what the following means:
For any combination of resource, operation, and request or response in the API, if a media type is specified as a key of the body property for that resource and operation and request or response, or if a media type is specified in the mediaType property, the body MUST conform to the specified media type.
Maybe we should describe that better, or we can remove that as we describe something similar (I guess) in a prior section
The media types expected from API requests that contain a body, and returned by API responses, can be defaulted by specifying the OPTIONAL mediaType property, so they do not need to be specified within every body definition.
It's not really clear to me what the following means:
Maybe we should describe that better, or we can remove that as we describe something similar (I guess) in a prior section