A fault handler is an optional part of a scope or invoke activity.

错误处理程序是范围或调用活动的可选部分。

youdao

Again, the return messages are an optional part of a sequence diagram.

此外，返回消息是序列图的一个可选择部分。

youdao

The WSDL document location is the only optional part of this endpoint definition.

WSDL文档位置是这个端点定义中惟一的可选项。

youdao

Part B is optional and pays a portion of non-hospital provided medical care, such as doctor visits and other outpatient services.

FORBES: Magazine Article

That part is not optional.

WSJ: The Feijoada From Ipanema

Part D is an optional insurance program that charges a monthly fee in exchange for prescription drug coverage.

FORBES: The ABCDs of Medicare