Created attachment 292058 [details]
Due to focus management issues in some browsers, one common approach for skip links is to link to a container with an id that also has an explicit tabindex attribute, making it focusable.
<a href="#content">Skip to main content</a>
<div id="content" tabindex="-1">...</div>
However, it seems that this sort of (fairly common) skip link pattern breaks in iOS10/VoiceOver/Safari. Specifically, it seems that if the target container has a tabindex attribute, VoiceOver does move the accessibility focus to the container, but announces nothing. But more worryingly, it then seems to ignore that entire target container - swiping left/right simply jumps over that container as if it wasn't in the document at all (though if you swipe long enough to get into the Safari UI and back, it seems to usually sort itself out again).
This is making fairly common skip links (for instance, those used in Bootstrap-based sites, if they follow the advice given in the BS documentation) completely unusable.
See attached test case and the video at https://www.youtube.com/watch?v=JUlSav9Nm_4 (the first skip link works, but the other two skip links - to a <div id="..." tabindex="0"> and <div id="..." tabindex="-1"> - exhibit this broken behavior)
Possibly worth noting: the reason why authors do set explicit tabindex is, among other things, this https://bugs.webkit.org/show_bug.cgi?id=116046 (to force keyboard interaction with skip links to work correctly)
Relating bug 158430