How to create a new submenu under the window menu

> Does menu include Windows child menu？

No; only CEP extensions will be placed on the Window -> Extensions menu. 

When I wrote "appropriate existing menus", I meant that C++ plugins would be added to the correct existing PPro menus; effects show up in the Effects list, transitions show up in the Effects list, Importers show up in the available import formats list, Exporters show up in the available export formats list.

PPro offers no capability for plugins or extensions to add menu items to arbitrary menus. 

The behavior you've described about PProPanel (menu item exists, but clicking it does nothing) is exactly the behavior you would see, if you had not enabled the loading of unsigned extensions; see the PProPanel readme for instructions on how to do that. 

hello Bruce Bullis

I have two questions that I would like to ask you.

1.“C++ plugins are added to the appropriate existing menus”
Does menu include Windows child menu？
If included, is there a demo for C++plugin that can refer to?

2. I downloaded the PProPanel instance and copied it to "\ CEP \ extensions". After PR started, there was an additional PProPanel (SDK sample panel) submenu in the extension menu. However, when I clicked on this menu, there was no response.

I am good at C++development and not very familiar with Java. Can you give me some help,How to pop up a window after Clicked on the “PProPanel (SDK sample panel)“ Menu

>Which demo can I use to implement adding a menu to an existing menu by C++plugin

None; it's not possible to modify or extend PPro's menus, via extension or plugin.

hello Bruce Bullis

Which demo can I use to implement adding a menu to an existing menu by C++plugin

Thsi sounds like a feature request. Moving to Ideas.