Drupal 8 field API vs. $form_state I am creating a field with Field API, and having it shown on user registration form. However, I need its value in order to make validation. For that purpose, I've used dpm($form_state) which gave me the dreadful, dreadful memory exhaustion error. I then used file_put_contents(' sites/default/files/debug.txt', print_r($form_state, TRUE)); which did not produce anything at all. I also tried a few suggestions made on IRC, among which are `$form_state->getValue(['field_tckn']). It seems I can't get what my field's value is, no matter what I do; and all I get is that the field is required when I fill it in; and I'm all out of ideas. Can you recommend anything else?
Taken from http://www.drupal.org/node/2350819:

If you import a field, it automatically goes into the disabled section because the fact that a field is shown or not is now stored in the entity display config entities, which fields do not now anything off. I should check what our default behavior is, but this is probably by design - which makes sense actually. And if not, it'll be a feature request.