title: element.scrollWidth + absolute magic
body: <p>I've found out that if container has absolutely positioned child, it's counted in <code>scrollWidth</code>, BUT only if it's on the right or bottom side of parent.
  Is it mentioned somewhere in the spec? </p>
  
  <p>Here is my fiddle
  <a href="https://jsfiddle.net/4m6nqq41/5/" rel="nofollow">https://jsfiddle.net/4m6nqq41/5/</a></p>
  
  <p>Also i've fount that <code>dir=rtl</code> changes horizontal behaviour vice versa.</p>