See-through is reference, not an effect
You want to read a reference while you type, not a frosted poster.
Translation, design callouts, a lecture beside notes: a translucent layer on top, words below still selectable. Opacity lives on the pop-out. Stop when you can read the draft. Do not fade until you cannot read either page.
Independent windows had this early. 2.0 did not put the slider on workspace tabs — the shell page fills the canvas. Reference happens after you pop out.
Opacity lives on the pop-out. The page underneath stays; the overlay is a see-through reference. Not a filter effect.
With pin
Pop out, set opacity, pin if you need. Opacity without pin loses the overlay when you switch apps. Pin without opacity blocks the draft completely unless you drag a gap.
Scrollbars follow window opacity so a solid bar does not ruin the overlay.
Do not
- Do not use opacity as wallpaper. If you cannot read, turn it back.
- Do not hunt a slider in the workspace. It is on the pop-out.
- If you cannot click through, use lock as widget. Do not set opacity to zero.
Tuck the overlay: Tuck to the edge.