The next document is created in a top-level window, that is, in the highest frame of the hierarchy; if the current frame is already a top window, the document is created in the current frame.
下一个文档在最高级别窗口中创建，即该层次结构的最高框架。如果当前框架已处于最高级别窗口，那么在当前框架中创建文档。