By editor, 24 December, 2015 Build a From from another Form Tags Drupal 8 Code Form Example : (From user login block)
By editor, 8 December, 2015 Form API Error - illegal selection Tags Drupal 8 Form Code Most likely, this error is due to dynamicaly changed options list. If you want to change the values of the options list, You must add: '#validated' => TRUE