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This could be a problem - easiest solution is to add a random token to the mime object that can be compared against so that only the originating AdvancedEditorAreaPane can accept the drag.
Good catch. I image this could be a feature in some applications... we shouldn't hard-code a solution excluding the possibility of moving tabs between windows. How about this: the drag object contains the id of the editor area that used to contain the tab, and the default drop target checks that it's the same as the target editor area. A trait could activate/deactivate the check.
I agree - we don't want to unnecessarily prevent the ability to drag tabs between windows. I'm just proposing it as a short-term fix since currently the behavior leads to a problem where the tab is moved, but the underlying editor doesn't properly migrate, and from then on whatever is being edited is not accessible (even upon restart of the application, unless a user deletes the application_memento and their session state). Once we've fixed it short term we can work out how to properly migrate editors. I tried a simplistic approach, but the way editors are currently designed there is too much wiring up that isn't properly replicated when the editor is moved to a new editor_area.