Form API Reference gives information about which properties to use for a form array, for Drupal 7.
Where can I see what properties I can use in
buildForm(array $form, FormStateInterface $form_state), such as #type, #title, #required? How can I know the other possible properties?
Actually I'm using the Drupal 7 information in Drupal 8, and it works, but there should/must be an updated page, I guess.