function doc(): Result {
    return $this->collectionBuilder()
      ->addTask($this->taskFilesystemStack()
        ->copy('CHANGELOG.md', 'doc/about/changelog.md')
        ->copy('LICENSE.md', 'doc/about/license.md'))
      ->addTask($this->taskExec('mkdocs build --config-file=etc/mkdocs.yaml'))
      ->addTask($this->taskFilesystemStack()
        ->remove(['doc/about/changelog.md', 'doc/about/license.md']))
      ->run();
  }