Created attachment 126502 [details]
If an app offers tabs, it should be possible to combine two individual app windows to a single window by dragging and dropping one window into the other and also to separate them again by the same action.
As a video says more than a thousand words, please have a look at the screen recording, how the Firefox browser does it.
I am not sure if this needs to solved at the Plasma, Qt or app level.
I could not accomplish this with Konsole, Dolphin, Kate or Okular.
(In reply to Christoph Feck from comment #2)
Thanks. The report has been opened 12 years ago ... I will lower my expectations. :-/