value of 1, the field will display a number that is 1 more than the current page number, but only if a page with that number exists. On the last page of the document, this same field will be empty.
值为 1 时，字段将显示一个比当前页码大 1 的数字，前提是该页码的页面存在。因此，在文档的最后一页上，此字段为空。