事实上，引用类型化元素，如conceptref和taskref，也可以在实体文件中定义，以便在其他专门化的子列表中重用它们。

In fact, reference typing elements such as conceptref and taskref may also be defined in the entities file for reuse in other specialized child lists.

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这些新元素中，只有 howto 需要在实体文件中声明，因此其他新建元素不能出现在 howto 元素的子列表中。

Of these new elements, only howto has been declared in the entities file because the other new elements should only appear in the child list of the howto element.

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