=== Problem
It's possible to click-through areas of the interface which are not expected to be clicked-through, leading to frustration.
This is not new, as far as I can remember this issue has been around since `Region Overlap` was introduced back in the days.
* Blender 2.79b
{F11320741, size=full, loop}
* Blender 3.0 alpha
{F11320307, size=full, loop}
In the 3D Viewport, the following parts marked in red are click-through:
{F11320410, size=full}
=== Proposal
In order to keep things feasible, preventing the following (in order of importance) areas from click-through would be great as a first milestone.
* **Panels and sub-panels** (background only, headers work properly and can't be clicked-through). //This is the highest priority//.
* **Sidebar Tabs**. Not only the background of the tabs area, but click-drag on tabs actually runs the active tool (Select Box by default).
* **Used header** area. I assume this can be tricky so it's listed last. But having some kind of mask around the widgets (including labels) to prevent click-through would solve the issue. For a first milestone, preventing clicking through the entire header/tool-settings bar would already be better than the current click-between-widgets behavior.
{F11320413, size=full}
There are other cases, but to keep things practical, covering what's in this task would be already a huge improvement in usability.