I was able to get it and
wow!!!! It's really great! Even better than my previous suggestion! Love it!

...Bravo Pierre!
Short description:
- Separation docked to the left: like in Alpha3, you can access each feature in full with tabs.
- Separation in use (takes full height): image preview part has no tab (good), while data part just show the needed tabs on the right (ie: Properties/histogram/Exif...).
- Separation docked to the right: image preview in full (without tabs).
It's so good that Menu item 'Use tabs' could be removed (I think the 'no tabs' setting made sense only with Image Preview... and it has no tab anymore when separation is docked to the right or in use

).
The only thing missing, in my opinion, is the 'Horizontal separation'.
This being said, it's not all that good: I confirm the tabs+separation bug... I couldn't get them back after unselecting 'use tabs'...
