Looks good to me, although any extra UI elements make it harder to implement. Can we get by with an entry in the editor window's system menu (which appears on Alt+Space, or right-click on the window icon)?

But CN already remembers "position of the last open editor windows". If you want to add note UIDs in the picture here, you need to be more specific ;)

Thanks for the clarifications, Thomas! Frankly, this seems a bit complicated scheme, and doesn't really correspond to the title of this ticket/idea. But let's wait till it gets at least 10 votes, after that we can get back to the discussion.

Probably you meant placement.<uid1> = <placement1>?  Because I don't see the placement itself in your scheme (if uid is the value - where are the coordinates?).
So basically you want CN to remember position of any note that has once been opened, and use the default positions for new/never opened notes. Is that correct?

Now it is clear, thanks. So you basically request the following scheme:
placement1 = <default pos for editor#1>
placement2 = <default pos for editor#2>
...
placement.uid[someuid1] = <pos for note with uid 1, takes precedence over placementN>
placement.uid[someuid2] = <pos for note with uid 2, takes precedence over placementN>

Is that correct?

Not at the same time, of course. Here's an example:
placement1.uid[1] = (0, 0, 100, 100)
placement2.uid[1] = (50, 50, 150, 150)

Now if you open the note with uid[1] as the first editor, it will be shown at (0, 0, 100, 100), but if another note is already open, it will be shown at (50, 50, 150, 150).

Any why not HTML? It's ok to have it inside of string literals.

Sorry for being slow here, I can't quite follow you.. So you suggest to keep placement1, placement2, etc, but also add the uid to it, so that we have placement1.uid1, placement1.uid2, placement2.uid1 ? Please keep in mind that placement2 = "second editor window". So that the one and same note can be opened at different positions depending on if there's already another editor window open. I guess this is not what you want, or maybe I'm wrong?

Thanks for the idea, Jww! Indeed tagging with middle-click is not as convenient as it could be.