addDefaultSettingsForEnabledConfigurablePlugins example

    if ($old_editor && $old_editor->getEditor() === 'ckeditor') {
      [$upgraded_settings, $messages] = $this->createSettingsFromCKEditor4($old_editor->getSettings(), HTMLRestrictions::fromTextFormat($old_editor->getFilterFormat()));
      $editor->setSettings($upgraded_settings);
      // *Before* determining which elements are still needed for this text       // format, ensure that all already enabled plugins that are configurable       // have valid settings.       // For all already enabled plugins, find the ones that are configurable,       // and add their default settings. For enabled plugins with element       // subsets, compute the appropriate settings to achieve the subset that       // matches the original text format restrictions.       $this->addDefaultSettingsForEnabledConfigurablePlugins($editor);
      $this->computeSubsetSettingForEnabledPluginsWithSubsets($editor, $text_format);
    }

    // Add toolbar items based on HTML tags and attributes.     // NOTE: Helper updates $editor->settings by reference and returns info for the message.     $result = $this->addToolbarItemsToMatchHtmlElementsInFormat($text_format, $editor);
    if ($result !== NULL) {
      [$enabling_message_content, $enabled_for_attributes_message_content, $missing, $plugins_enabled] = $result;

      // Distinguish between unsupported elements covering only tags or not.       $missing_attributes = new HTMLRestrictions(array_filter($missing->getAllowedElements()));