What are the 'main' and 'alternative' KDE task switchers?

Project:Linux software
Component:Documentation
Category:feature request
Priority:normal
Assigned:Unassigned
Status:active
Related pages:#226: KDE System Settings
Description

In KDE system settings > Workspace appearance and behaviour > window behaviour > task switcher >
there are two sets: 'main' and 'alternative'.
The KDE documentation does not explain what those two sets are for, how to enable one instead of the other, etc...
https://docs.kde.org/stable/en/kde-workspace/kcontrol/kwintabbox/
https://userbase.kde.org/System_Settings/Window_Behaviour