- the alt query parameter on a request URL, or
- an Accept: header of the http request.
If the EDAA receiving the above request supports the JSON serialization format, it would return a collection of instance representations in JSON. EDAA conventions on JSON describes how collections of resource instances are represented in JSON in EDAA.
If the EDAA doesn't support JSON, it will return an error, http code 400 (bad request).
GET /instances Accept: application/json