Is the use of $ref compliant with OpenAPI 3.0.3 specification?

I don't see mention of support in the OpenAPI [specification](https://swagger.io/specification/v3/) 3.0.3 or 3.1.0 for using $ref at the levels shown below in this top level index.yml:

https://github.com/googlemaps/openapi-specification/blob/2e52e97deaf7e482ef6da505e68a06d5c1abedf7/specification/index.yml#L22-L28

The reason I raise this is that I don't see these fields available in the results from parsing your specification with the java artifact io.swagger.parser.v3:swagger-parser:2.1.13 and after checking the specification I'm supposing your yaml specification is not compliant with the standard. Is that the case?