LocalActionManager::$defaults

protected $defaults = array(
  // The plugin id. Set by the plugin system based on the top-level YAML key.
  'id' => NULL,
  // The static title for the local action.
  'title' => '',
  // The weight of the local action.
  'weight' => NULL,
  // (Required) the route name used to generate a link.
  'route_name' => NULL,
  // Default route parameters for generating links.
  'route_parameters' => array(),
  // Associative array of link options.
  'options' => array(),
  // The route names where this local action appears.
  'appears_on' => array(),
  // Default class for local action implementations.
  'class' => 'Drupal\Core\Menu\LocalActionDefault',
);