text representation.
                * `externalDocs`: Additional external documentation for this tag. If
                    provided, it would contain a `dict` with:
                    * `description`: A short description of the target documentation.
                        [CommonMark syntax](https://commonmark.org/) MAY be used for
                        rich text representation.

                be a Pydantic model, it could be other things, like a `list`, `dict`,
                etc.

                It will be used for:

                * Documentation: the generated OpenAPI (and the UI at `/docs`) will
                    show it as the response (JSON Schema).
                * Serialization: you could return an arbitrary object and the