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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列表1新建HelloWorld类的代码。

Listing 1. Code for the newly created HelloWorld class.

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可考虑新建一个“20首最有感觉的歌曲”的播放列表。

Consider creating a playlist of your Top 20 Feel Good Songs.

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