It can also save time, if it turns out (as it often does) that the only thing done with the node-set is to test whether it is empty, or to get the value of its first element.
它还可以节省时间，如果对于节点集的唯一操作就是测试它是否是空的(通常是这种情况)，或者对它的第一个元素进行赋值。
You can test for them explicitly or rely on PHP to return a default empty value when you reference them.
您可以显式地对它们进行检测，或在您引用它们时让 PHP返回缺省的空值。
Groundless and empty theory can never stand the test of practice.
毫无实践的虚无理论，根本经不起验证.自谓迷徒，实乃自以为是看破时间万物的一个傻孩子。
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