In the documentation for #value, the Drupal 7 documentation contains the following note:
Note that as of Drupal 6, you can also simply store arbitrary variables in
$form['#foo']instead, as long as
'#foo'does not conflict with any other internal property of the Form API.
Is that still possible, in Drupal 8?
I looked at the documentation for the
Value class, but the note given for Drupal 7 is not present.
I know Drupal adds
$form['#token'] to forms, but I take it is a special case Drupal handles in a particular way.