https://drafts.csswg.org/css2/#visibility defines that I can make invisible areas (visibility:hidden) visible with visibility:visible.

The invisible areas do not show up in the browsers Accessibility API tree. The visible ones do. This causes certain nested elements to become invalid for the API (e.g. table cells without a table, because the table is marked with visibility:hidden, but the table cells are marked with visibility:visible).

I suggest to include a warning in the specification that visibility:visible must not be used with nested elements.

Otherwise, there will be a broken tree in the Accessibility API and incorrect output from screen readers