camera window AND 3D window

Look at the attached screenshot. It is taken from a The creator has a few windows open.

The changes he makes in the 3D-window can be seen in the bottom-left window.

I tried to recreate this: I duplicated the existing 3D-window. Made it smaller. Then put it on camera view.

But as soon as I click in the 3D-window, the camera-view window disappears from screen.

Question: how to do this? 3D-window and Camera-window, so that changes to the 3D-window can be immediately seen in the camera-window. Can the camera-window be docked?

You need to split the 3D viewport:

This leaves you with three 3D viewports, which you can now set to whatever view you want. Unless you save you user preferences, this will not be permanent.

Briljant. That worked. Thank you very much,IkariShinji.