I can move a window containing multiple tabs to main window, but I can not move them from main application to another window.
Let me explain;
Consider I have two monitor and I moved attribute tables to second monitor. Now I have another window having many attribute table tabs in second monitor. I can move and dock this window including all the tabs to main application window. But I cannot do vice-versa. I have to move tabs one by one.
It would better to give an option to drag and drop entire group to another window.