protected function config($name) {

.....

if (in_array($name, $this->getEditableConfigNames())) {

      // Get a mutable object from the factory.

      $config = $config_factory->getEditable($name);

    }

    else {

      $config = $config_factory->get($name);

    }

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这个是怎么回事呢？

当在form类下调用config方法时，

当name在getEditableConfigNames所返回的数组里面，

则调用geteditable表示可以修改，