SUMMARY In KDE 4, there used to be a quite handy feature for grouping different windows (across applications as well). They appear as tabs on the "same window". But this is missing in Plasma 5, AFAIK. Earlier releases of Plasma 5 had this in the errata (e.g. https://community.kde.org/Plasma/5.10_Errata ). But that page is no longer published for newer versions. Is this no longer wanting to be supported? Or is this simply not prioritized?
>Is this no longer wanting to be supported no. With the rise of client-side-decorations it would be a feature that would not work reliably, the user-experience would be unpredictable at best.