+ $element['collapsible'] = [
+ '#type' => 'checkbox',
+ '#title' => $this->t('Collapsible'),
+ '#default_value' => $this->getSetting('collapsible'),
+ ];
+ $element['collapsed'] = [
+ '#type' => 'checkbox',
+ '#title' => $this->t('Collapsed by default'),
+ '#default_value' => $this->getSetting('collapsed'),
+ '#states' => [
+ 'visible' => [
+ ':input[name="' . $states_prefix . '[collapsible]"]' => ['checked' => TRUE],
+ ],
+ ],
+ ];