"Hierarchy" implies a tree structure, where each process belongs to a higher level process (except for processes at the highest level).
“层次结构”意味着是树形结构，每个流程属于较高级别的流程(最高级别的流程除外)。
Discovering the entire inheritance tree structure from an existing system is particularly useful, because it helps you uncover what the top-level class is and what subclasses are in the tree.
从一个已存在系统中发现整个的继承树结构是相当有用的，因为它能向您揭露在树中什么是顶级类以及什么是子类。
However, if you have two elements where there is no direct parent-child relationship and they do not lie on the same level in the tree structure, their event firing sequence is not fixed.
但是，如果您拥有两个没有上下级关系的元素，而且它们在树形结构中不是同一层次，那么它们的事件引发序列就是不同的。
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