public static function el(array &$form, FormStateInterface $form_state) {
    $trigger = $form_state->getTriggeringElement();
    return NestedArray::getValue($form, array_slice($trigger['#array_parents'], 0, -1));
  }
public static function el(array &$form, FormStateInterface $form_state) {
    $trigger = $form_state->getTriggeringElement();
    return NestedArray::getValue($form, array_slice($trigger['#array_parents'], 0, -1));
  }
public static function el ( array & $ form , FormStateInterface $ form_state ) { $ trigger = $ form_state -> getTriggeringElement ( ) ; return NestedArray :: getValue ( $ form , array_slice ( $ trigger [ '#array_parents' ] , 0 , - 1 ) ) ; }
Returns the root element for a triggering element.

@param array $form
The complete form.
@param \Drupal\Core\Form\FormStateInterface $form_state
The current form state.

@return array
The root element that contains the triggering element.
Returns the root element for a triggering element .