可以对任何元素声明名称空间，从而允许在由该元素及其所有子元素定义的子树内识别它。

A namespace can be declared on any element, allowing it to be recognized within the sub-tree defined by that element and all its children.

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这里定义了一个简单的 Perl 子例程向树中的一个节点增加子元素，然后用它构造表示单个新宠物的子树。

You define a simple Perl subroutine to add a subelement to a node in the tree and then use this to construct the subtree representing an individual pet.

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帮助你的孩子树立责任心——要求他帮着做家务，如收拾桌子。

Help your child develop a sense of responsibility-ask him to help with household tasks, such as setting the table.

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