Right!

And what about the use of this function ?

formRenderField('fieldToUpdate', ['useContainer'=>false])

Sorry, I missed this last question. Did you find the answer?

No I sticked to your code, I saw an example with this function, but didn't find any good justify in the documentation...

Thanks

You mean this:

$fieldMarkup = $form->renderField($fieldName, ['useContainer' => true]);

What do you not understand?

I was wondering if there is a difference with this function :

https://octobercms.com/docs/api#formrenderfield

Incremental said:

I was wondering if there is a difference with this function :

https://octobercms.com/docs/api#formrenderfield

Not sure, but I think the one you reference is when you don't have the Form widget object. it basically does the same thing.

If you look at the source code, one calls the other:

public function  formRenderField($name, $options = [])
{
    return $this->formWidget->renderField($name, $options);
}

ref. https://github.com/octobercms/october/blob/a43833d511ec1700ce4ed2a13e573fcbf87c7bee/modules/backend/behaviors/FormController.php#L554,L557