Note that this is not compatible with OpenAPI 3.0.3 which states that the $ref should replace everything. However, in OpenAPI 3.1.0 will be compatible to JSON schema which allows in 2019-09 to add any keywords next to a $ref. In older versions JSON schema also didn't have this but they figured out that it's more intuitive like this rather than using allOf as a workaround. We already used this syntax for adding defaults, so we will continue to be slightly ahead of OpenAPI (that is until 3.1.0 is released which is currently in RC0).
Note that this is not compatible with OpenAPI 3.0.3 which states that the
$refshould replace everything. However, in OpenAPI 3.1.0 will be compatible to JSON schema which allows in 2019-09 to add any keywords next to a$ref. In older versions JSON schema also didn't have this but they figured out that it's more intuitive like this rather than usingallOfas a workaround. We already used this syntax for addingdefaults, so we will continue to be slightly ahead of OpenAPI (that is until 3.1.0 is released which is currently in RC0).