docs: def angularFrontendAppDir(self) -> str:
          """ Angular Frontend Dir
  
          This directory will be linked into the angular app when it is compiled.
  
          :return: The absolute path of the Angular2 app directory.
          """
          relDir = self._packageCfg.config.plugin.title(require_string)
          dir = os.path.join(self._pluginRoot, relDir)
          if not os.path.isdir(dir): raise NotADirectoryError(dir)
          return dir