title: Determine why an element receives focus?
body: <p>We have an app that manages focus pretty meticulously and recently I've found a bug that causes some element to become focused unexpectedly. I've been pulling my hair out looking for the source of this issue. Is there some way we can determine <em>why</em> an element is being focused/what code is initiating that?</p>
  <p>I've added a <code>focus</code> event listener, but I can't find any clues even in the <code>event</code> object it receives.</p>
  <p>Does anyone have any ideas about how to track this down? We're using React, in case there might be any hidden tricks or tools I'm overlooking.</p>