Also has three optional sub-elements.

还有三个可选的子元素。

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Id, price and quantity - sub-elements of item.

price和quantity——项目的子元素。

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The various sub-elements occur in the listed order (if at all).

各种子元素以列出的顺序（如果有的话）出现。

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The various sub-elements occur in the listed order (if at all).

各种子元素以列出的顺序（如果有的话）出现。

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