Have an automatic API documentation web user interface.

### <a href="https://flask.palletsprojects.com" class="external-link" target="_blank">Flask</a>

Flask is a "microframework", it doesn't include database integrations nor many of the things that come by default in Django.

This simplicity and flexibility allow doing things like using NoSQL databases as the main data storage system.

* A particular program while it is **running** on the operating system.
    * This doesn't refer to the file, nor to the code, it refers **specifically** to the thing that is being **executed** and managed by the operating system.
* Any program, any code, **can only do things** when it is being **executed**. So, when there's a **process running**.

But now you know how it works, so you can use relative imports in your own apps no matter how complex they are. 🤓

### Add some custom `tags`, `responses`, and `dependencies`

We are not adding the prefix `/items` nor the `tags=["items"]` to each *path operation* because we added them to the `APIRouter`.

            Doc(
                """
                The version of the API.

                **Note** This is the version of your application, not the version of
                the OpenAPI specification nor the version of FastAPI being used.

                It will be added to the generated OpenAPI (e.g. visible at `/docs`).

                Read more in the

And you could do this even if the data type in the request is not JSON.

For example, in this application we don't use FastAPI's integrated functionality to extract the JSON Schema from Pydantic models nor the automatic validation for JSON. In fact, we are declaring the request content type as YAML, not JSON:

=== "Pydantic v2"

    ```Python hl_lines="17-22  24"