title: Potential bug with HTML drag/drop and event bubbling
body: <p>I noticed that when there's a div inside a div that's handling dragenter/leave events, dragging over the inner div causes the outer div to trigger <code>dragleave</code>. But this only happens when the outer div is <code>position: fixed</code>. Otherwise, dragging over the child/inner div properly bubbles up to its parent.</p>
  
  <p>Example: <a href="https://jsfiddle.net/ffxsam/L2mvbo2t/" rel="nofollow">https://jsfiddle.net/ffxsam/L2mvbo2t/</a></p>
  
  <p>Drag a file over the output pane and you'll see the dropzone show up. If you continue to drag over the "Uh oh" text, the dropzone vanishes. Comment out the <code>position: fixed</code> line, then try again, and you'll see if you drag over "Uh oh," the dropzone remains.</p>
  
  <p>Is this a bug? Actually, I just realized that in Firefox, the <code>dragleave</code> gets triggered as I move over the inner div, regardless of <code>position</code>. How can I work around this?</p>