The Form component documentation at http://symfony.com/doc/current/components/form.html does not explain how and why users can define their forms as PHP classes.

The main article explains how to build and use a form right inside the controller code, with no mention of Form classes or the $formFactory->createForm() method.

The "Learn more" links don't mention "Forms as classes".

The first "Learn more" article (http://symfony.com/doc/2.8/form/action_method.html) mentions "When using a form type class...", but at that point, the reader hasn't been presented with that option and, likely, does not understand the mention.

None of the "Learn more" articles, as far as I can say, explain how to build and use a form as a PHP class.

Nevertheless, the "Best Practices - Forms" article (https://symfony.com/doc/current/best_practices/forms.html) recommends "defining forms as PHP classes." (and explains how to do that in a few lines and an example).

I think there's an article missing here, right at the top of the "Learn more" section of the Form component, which explains "How to define your forms as PHP classes".