Bug 995035 - Hide invisible parts of SMS app from screen reader.

> Actually hiding the elements (as opposed to aria-hidden) gives a better user experience as the accessible tree state changes and the user is notified by having the cursor moved.

I think we move the cursor programmatically most of the time; if we don't in some cases, let's change it.

> aria-hidden, could be used as a last resort, but I am also concerned with the complexity of the navigation.js code, and not getting all cases right.

I think the easiest is to do the changes directly in the panels' afterEnter/beforeLeave (but then there will be a moment where both panels will be hidden; maybe better to use beforeEnter/afterLeave ? Or a mix of both ?). The panels know their container dom node, while the navigation code only knows the javascript object.

> Doing it in CSS assures that we are consistent with the visual state.

I agree with you. As I said on the bug, in long-term, with Haida and sheets, it will probably be possible to do it, but with the current state of the app I think it's not.