So make it opt-in, and highly visible to the user when it happens. I get a nag screen when videos in the browser go full screen, telling me loud and clear that

So make it opt-in, and highly visible to the user when it happens. I get a nag screen when videos in the browser go full screen, telling me loud and clear that expected behaviour is changing and telling me how to get control back. When a website overrides keyboard controls, the first I know about it is when I can't scroll properly, or switch to another tab, or go back, or close the window that's yelling at me and making my machine thrash ... Disruptively changing modes without notification violates fundamental rules of interaction design, affordances and basic security. How is that okay?