This method tells you all information you need to know: whether one node is descendant of an ancestor of the other, whether it is before or after, and so on.
这个方法告诉您所有想知道的信息：一个节点是否是另一个节点的祖先的后代，它是在前面还是后面呢，等等。
If you must use descendant selectors, prefer child selectors, which at least only require evaluation of one additional node, not all the intermediate nodes up to an ancestor.
如果您必须使用后代选择器，尽量使用子代选择器，这最少只需评估一个额外的节点，而非中间直至祖先的所有节点。
Every simple path from a node to a descendant leaf contains the same number of black nodes.
从节点到后代叶节点的所有简单路径都包含相同的黑节点数。
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