Some optional items that I found useful are as follows.

一些可选项目，我发现有用的内容如下。

youdao

Within these directories, OS X expects to find certain mandatory subdirectories and files (and various optional items).

在这些目录中，OS X 希望找到特定的托管子目录和文件（以及各种不同的可选项）。

youdao

The expressions surrounded by brackets (" [" and "] ") represent optional items that may be required depending on the previous choices.

方括号(“[”和“]”)包括的表达式表示一些可选项目，是否需要取决于前面的选择。

youdao

Simply select the type of invitation, enter your guests' e-mail addresses, create an "items to bring" list (optional), then send.

FORBES: Party Planning

After all, the items can still be unlocked through traditional means, and the system is entirely optional.

FORBES: Microtransactions are the New Cheat Codes, and Why that's Sad