Keyboard scope

By default the keys listen on the whole page, which suits a full-window viewer. A viewer embedded in a page with text around it should pass keys: 'focus': the keys then act only while the viewer’s element has focus, so the arrow keys and Space still scroll the page otherwise. The element gets tabindex="0" (unless it has one) and takes focus on a click or tap, without matching :focus-visible, so a keyboard focus ring styled by the page shows only when Tab reaches it. Held keys are released when focus leaves. keys: false turns the keyboard off.