Results

    '#description' => t('A local file system path where blacksmith source files will be stored.'),
    '#required' => TRUE,
    '#after_build' => ['system_check_directory'],
    '#weight' => 20,
  ];

  if ($form['file_default_scheme']) {
    $form['file_default_scheme']['#weight'] = 30;
  }

 *   The current state of the form.
 *
 * @see \system_check_directory()
 */
function content_packager_check_directory_form(array $form_element, FormStateInterface $form_state) {
  $scheme = $form_element['package_scheme']['#value'];
  $base_folder = $form_element['base_folder']['#value'];
  $destination = $form_element['package_destination']['#value'];

      '#maxlength' => 255,
      '#description' => t('An existing local file system path for storing Developer Documentation files. It should be writable by Drupal and not accessible over the web. See the online handbook for <a href="@handbook">more information about securing private files</a>.', array('@handbook' => 'http://drupal.org/documentation/modules/file')),
      '#after_build' => array('system_check_directory'),
    );

    return parent::buildForm($form, $form_state);
  }

  /**

          '#size' => 60,
          '#maxlength' => 128,
          '#after_build' => array('system_check_directory'),
          '#description' => t('The name of a temporary directory, <b>relative to you drupal installation</b>, where I\'ll temporarily store user jpeg files (a.k.a avatars), if necessary. It is not necessary <b>not</b> to prepend or append slashes (/).'));

  /**
   * ADDRESSBOOK SETTINGS
   */
  $form['addressbook'] = array('#type' => 'fieldset',

      '#maxlength' => 255,
      '#description' => t('A alternative local file system path where temporary files will be stored. This directory should not be accessible over the web.'),
      '#after_build' => ['system_check_directory'],
    ];

    $form['#submit'][] = 'alt_stream_wrappers_form_system_file_system_settings_submit';
}

/**

      'theme_system_themes_form', 'system_help', 'system_theme', 'system_perm', 'system_elements',
      'system_menu', 'system_init', 'system_user', 'system_block', 'system_admin_menu_block',
      'system_admin_theme_submit', 'system_theme_select_form', 'system_check_directory',
      'system_get_files_database', 'system_theme_default', 'system_theme_data', '_system_theme_data',
      'system_find_base_theme', 'system_region_list', 'system_default_region', 'system_initialize_theme_blocks',
      'system_settings_form', 'system_settings_form_submit', '_system_sort_requirements',
      'system_node_type', 'confirm_form', 'system_admin_compact_mode', 'system_get_module_admin_tasks',
      'system_cron', 'system_hook_info', 'system_action_info', 'system_actions_manage',
      'system_actions_manage_form', 'system_actions_manage_form_submit', 'system_actions_configure',

      'system_clean_url_settings', 'system_error_reporting_settings', 'system_performance_settings',
      'system_file_system_settings', 'system_image_toolkit_settings', 'system_rss_feeds_settings',
      'system_date_time_settings', 'system_site_maintenance_settings', 'system_check_directory',
      'system_get_files_database', 'system_theme_data', 'system_region_list', 'system_default_region',
      'system_initialize_theme_blocks', 'system_settings_form', 'system_theme_settings_submit',
      'system_settings_form_submit', 'system_themes', 'theme_system_themes', 'system_themes_submit',
      'system_modules', 'system_modules_disable', 'system_modules_confirm_form', 'system_module_build_dependencies',
      'system_modules_submit', 'theme_system_modules', 'system_modules_uninstall', 'system_modules_uninstall_confirm_form',
      'theme_system_modules_uninstall', 'system_modules_uninstall_validate', 'system_modules_uninstall_submit',

      '#required' => TRUE,
      '#default_value' => $this->configuration['source_directory'],
      '#after_build' => ['system_check_directory'],
    ];
    return $form;
  }

}

      '#name' => 'file_public_path',
      '#description' => $this->t('A local file system path where library files will be stored. This directory should be accessible over the web.'),
      '#after_build' => ['system_check_directory'],
      '#default_value' => $settings['libraries_path'],
    ];

    return parent::buildForm($form, $form_state);
  }