<label> elements with tabindex="-1" are not focusable via JavaScript. Can reproduce an all Safari versions I have at hand (Nightly, Safari 10.0.1, iOS 10.2). See https://jsfiddle.net/gigasoft/smh5gwar/ for a simple test case. Related to: https://bugs.webkit.org/show_bug.cgi?id=102780
I think Ryosuke has worked on this area recently?
*** This bug has been marked as a duplicate of bug 102780 ***