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Description
If the WindowProxy is a nested browsing context, you get a window handle, except you can't actually use it for anything (e.g., you can't use it to switch the current browsing context). Having an opaque string that's only useful for comparing it doesn't seem like it is very useful?
(Technically, you could, by going to its top-level browsing context and then switching to every frame until you find one with the same window handle.)
As for a use-case: I have a message
event and I want to switch the current browsing context to e.source
to react to that message.