The fourth predicate $i/*/price = 29 looks for price elements under any root element, not just "book."

第四个谓词 $i/*/price = 29 将查找任何根元素下的 price 元素，而不仅仅是在 “book” 元素下的。

youdao

For example, if you plan on writing four chapters of your soon-to-be-published book in a month, it is not until the fourth week that you'll consider yourself actually procrastinating.

比如，你即将出版的书，如果计划在一个月里写四个章节，很可能直到第四周你才会意识到自己一直在拖延。

youdao