Inconsistency for accepted keys in Component fix fields

[lasconic]

In the 3.1 spec one can read the following

All the fixed fields declared above are objects that MUST use keys 
that match the regular expression: ^[a-zA-Z0-9\.\-_]+$.

However, most of the fixed fields accept a Reference Object with the key $ref which doesn't match the regular expression.

This inconsistency or lack of precision causes some tools to enforce the regular expression blindly and do not consider $ref under parameters for example as a valid OpenAPI document.
See for example : OpenAPITools/openapi-generator#11151

[hkosova]

components:
  schemas:
    SchemaName:    # <---- It's about these keys
      ...

  parameters:
    limit:         # <----
      ...

The example from OpenAPITools/openapi-generator#11151

components:
  schemas:
    $ref: './definitions/_index.yaml'

is not valid OpenAPI syntax because $ref is not allowed directly under components.<type>, it's only allowed under components.<type>.<name>.

Some tools (such as bundlers/dereferencers) choose to support $refs in arbitrary places. In this case, you'd have to pre-process the file with the corresponding bundler/dereferencer to resolve non-standard $refs before using the file with OpenAPI-compliant tools.

[lasconic]

Thank you for your answer.
OK, I reread the spec and I was mislead by

Map[string, Response Object | Reference Object]

Now I get it.