Hi, noticed that the [jsonapi schema](https://github.com/json-api/json-api/blob/v1.1rc3/schema) does not have the $id property. just curious if that's intended design? The reason for asking is that currently, to reference the spec in something like following, I would need to add an $id property to the jsonapi schema? ``` "allOf": [ { "$ref": "http://jsonapi.org/schema#/definitions/success" }, { "$ref": "#/definitions/myDomainResponse" } ], ```