I thought of that. Visibility testing would always report as visible, and testing the vertical scroll position would always report zero, and the user can config

I thought of that. Visibility testing would always report as visible, and testing the vertical scroll position would always report zero, and the user can configure in what cases mouse location can be tested and how. (Document scripts should actually be disabled by default I think, and what features are available (and in some cases, spoofed) depends on user settings which can be global or specific to URL patterns. For example, full mouse and keyboard events might be available only for activated <canvas> elements when quote mode is active, and other than that is only used to calculate form fields, perhaps.)