For example, in an HTTP Bearer token scheme, the client will send a header
    like:

    ```
    Authorization: Bearer deadbeef12346
    ```

    In this case:

    * `scheme` will have the value `"Bearer"`
    * `credentials` will have the value `"deadbeef12346"`
    """

    scheme: Annotated[
        str,
        Doc(
            """

            """
            'Whitelist' validation step. The parameter field will be the single one
            allowed by the alias or set of aliases defined.
            """
        ),
    ] = None,
    serialization_alias: Annotated[
        Union[str, None],
        Doc(
            """
            'Blacklist' validation step. The vanilla parameter field will be the

                Security scheme name.

                It will be included in the generated OpenAPI (e.g. visible at `/docs`).
                """
            ),
        ] = None,
        description: Annotated[
            Optional[str],
            Doc(
                """
                Security scheme description.

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

) -> Union[DefaultPlaceholder, DefaultType]:
    """
    Pass items or `DefaultPlaceholder`s by descending priority.

    The first one to _not_ be a `DefaultPlaceholder` will be returned.

    Otherwise, the first item (a `DefaultPlaceholder`) will be returned.
    """
    items = (first_item,) + extra_items
    for item in items:
        if not isinstance(item, DefaultPlaceholder):
            return item

from fastapi import FastAPI

description = """
ChimichangApp API helps you do awesome stuff. 🚀

## Items

You can **read items**.

## Users

You will be able to:

* **Create users** (_not implemented_).
* **Read users** (_not implemented_).
"""

app = FastAPI(
    title="ChimichangApp",
    description=description,
    summary="Deadpool's favorite app. Nuff said.",
    version="0.0.1",

            "title": "ChimichangApp",
            "summary": "Deadpool's favorite app. Nuff said.",
            "description": "\nChimichangApp API helps you do awesome stuff. 🚀\n\n## Items\n\nYou can **read items**.\n\n## Users\n\nYou will be able to:\n\n* **Create users** (_not implemented_).\n* **Read users** (_not implemented_).\n",
            "termsOfService": "http://example.com/terms/",
            "contact": {
                "name": "Deadpoolio the Amazing",

                    "description": 'Create an invoice.\n\nThis will (let\'s imagine) let the API user (some external developer) create an\ninvoice.\n\nAnd this path operation will:\n\n* Send the invoice to the client.\n* Collect the money from the client.\n* Send a notification back to the API user (the external developer), as a callback.\n    * At this point is that the API will somehow send a POST request to the\n        external API with the notification of the invoice...

from fastapi import FastAPI

description = """
ChimichangApp API helps you do awesome stuff. 🚀

## Items

You can **read items**.

## Users

You will be able to:

* **Create users** (_not implemented_).
* **Read users** (_not implemented_).
"""

app = FastAPI(
    title="ChimichangApp",
    description=description,
    summary="Deadpool's favorite app. Nuff said.",
    version="0.0.1",

                Security scheme name.

                It will be included in the generated OpenAPI (e.g. visible at `/docs`).
                """
            ),
        ] = None,
        description: Annotated[
            Optional[str],
            Doc(
                """
                Security scheme description.

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

            "title": "ChimichangApp",
            "summary": "Deadpool's favorite app. Nuff said.",
            "description": "\nChimichangApp API helps you do awesome stuff. 🚀\n\n## Items\n\nYou can **read items**.\n\n## Users\n\nYou will be able to:\n\n* **Create users** (_not implemented_).\n* **Read users** (_not implemented_).\n",
            "termsOfService": "http://example.com/terms/",
            "contact": {
                "name": "Deadpoolio the Amazing",