```Python hl_lines="10"
{!../../../docs_src/query_params_str_validations/tutorial003.py!}
```

## Adicionando expressões regulares

Você pode definir uma <abbr title="Uma expressão regular, regex ou regexp é uma sequência de caracteres que define um parâmetro de busca para textos.">expressão regular</abbr> que combine com um padrão esperado pelo parâmetro:

```Python hl_lines="11"

That's what makes it possible to have multiple automatic interactive documentation interfaces, code generation, etc.

OpenAPI has a way to define multiple security "schemes".

By using them, you can take advantage of all these standard-based tools, including these interactive documentation systems.

OpenAPI defines the following security schemes:

* `apiKey`: an application specific key that can come from:
    * A query parameter.
    * A header.

# `HTTPConnection` class

When you want to define dependencies that should be compatible with both HTTP and WebSockets, you can define a parameter that takes an `HTTPConnection` instead of a `Request` or a `WebSocket`.

You can import it from `fastapi.requests`:

```python
from fastapi.requests import HTTPConnection
```

    * Because pydantic data structures are just instances of classes you define; auto-completion, linting, mypy and your intuition should all work properly with your validated data.
* Validate **complex structures**:
    * Use of hierarchical Pydantic models, Python `typing`’s `List` and `Dict`, etc.
    * And validators allow complex data schemas to be clearly and easily defined, checked and documented as JSON Schema.

# Header Parameters

You can define Header parameters the same way you define `Query`, `Path` and `Cookie` parameters.

## Import `Header`

First import `Header`:

=== "Python 3.10+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/header_params/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/header_params/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

#### "*Schema*"

Um "*schema*" é uma definição ou descrição de algo. Não o código que o implementa, mas apenas uma descrição abstrata.

#### API "*schema*"

Nesse caso, <a href="https://github.com/OAI/OpenAPI-Specification" class="external-link" target="_blank">OpenAPI</a> é uma especificação que determina como definir um *schema* da sua API.

Then I contributed to it, to make it fully compliant with JSON Schema, to support different ways to define constraint declarations, and to improve editor support (type checks, autocompletion) based on the tests in several editors.

# Background Tasks

You can define background tasks to be run *after* returning a response.

This is useful for operations that need to happen after a request, but that the client doesn't really have to be waiting for the operation to complete before receiving the response.

This includes, for example:

* Email notifications sent after performing an action:

OpenAPI tem uma forma para definir múltiplos “esquemas” de segurança.

Por usá-los, você pode ter vantagens de todas essas ferramentas baseadas nos padrões, incluindo os sistemas de documentação interativa.

OpenAPI define os seguintes esquemas de segurança:

* `apiKey`: uma chave específica de aplicação que pode vir de:
    * Um parâmetro query.

So, you could add additional data to the automatically generated schema.

For example, you could decide to read and validate the request with your own code, without using the automatic features of FastAPI with Pydantic, but you could still want to define the request in the OpenAPI schema.

You could do that with `openapi_extra`:

```Python hl_lines="20-37  39-40"