in any case, i agree that there's a lot going on to add affordances for keyboard users that screenreader users don't need. screenreaders would just need the <nav> element (probably should be aria-labeled too) and the <ul> link list.

it's neat but a little convoluted. i'd also vote for using a <button> rather than a checkbox plus anchors, but buttons do have technical limitations (as noted elsewhere) that browser engines should fix (similar to how dialog elements are now nearly javascript-less, only requiring a `showModal()` call to open), rather than having to have authors work around them.