```

Notice that the default value is still `None`, so the parameter is still optional.

But now, having `Query(max_length=50)` inside of `Annotated`, we are telling FastAPI that we want it to extract this value from the query parameters (this would have been the default anyway 🤷) and that we want to have **additional validation** for this value (that's why we do this, to get the additional validation). 😎

    ```Python hl_lines="7"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_py310.py!}
    ```

## 🚮 🥔 🧬

👆 💪 🔬 <abbr title="A regular expression, regex or regexp is a sequence of characters that define a search pattern for strings.">🥔 🧬</abbr> 👈 🔢 🔜 🏏:

=== "🐍 3️⃣.6️⃣ &amp; 🔛"

    ```Python hl_lines="11"
    {!> ../../../docs_src/query_params_str_validations/tutorial004.py!}
    ```

    ```

Dieses bestimmte reguläre Suchmuster prüft, ob der erhaltene Parameter-Wert:

* `^`: mit den nachfolgenden Zeichen startet, keine Zeichen davor hat.
* `fixedquery`: den exakten Text `fixedquery` hat.
* `$`: danach endet, keine weiteren Zeichen hat als `fixedquery`.