Created attachment 151919 [details]
Screenshot of two-panel setup illustrating the feature request

This is a feature request independent of the distro or plasma version, hence I will not use the standard template for the report.

Background:
When a multi-panel setup is used in which two panels are located on adjacent screen edges (eg. a Unity style setup, see the attached image), the panels have no collision detection and will overlap when their lengths are maximized. Moreover, this overlap will not be consistent as panels seem to have their own focus rules and if a widget or the panel itself is clicked, that panel will be raised over the other.

Non-overlapping panels can only be forced by manually resizing one panel, however it is difficult to do this exactly, i.e. without having a small gap between the two panels or them slightly overlapping. Furthemore, even if the proper panel size is gauged appropriately, due to the focus behaviour of panels, there are still visual inconsistencies, for example in the setup presented in the attached screenshot, if the top panel is focused, its shadow will dominate the left panel, but if the left panel is clicked then the top panel's shadow will go underneath it. Admittedly, this is a minor issue, but still noticable and annoying.

Feature request:
It would be nice if it would be possible to set up intersection rules for panels controlling how the panels should behave when they would overlap.
As an example for the setup in the attached screenshot, it should be possible to tell Plasma that I want the top panel to be "dominant" over the left panel. In this case, the top panel would always have focus over the left panel and the left panel - in its maximized state - would extend only until it collides precisely with the top panel, but will not go underneath it.