This is an attempt to synchronize editors between workspaces.
To make this possible, the desired areas are marked with slots that determine which area in one workspace corresponds to the area in another workspace. This design works well for 3D-view, 2D-editors, but not for Outliner unfortunately.
Demo, how it works:
I think this feature is very lacking, requests for it were on a blender.today
Not sure who to set for code review, so I set like D6262, looks similar (correct me, if I'm wrong)