[css-position-3] Note that the root always forms a stacking context. w3c#8353

Author: fantasai

css-position-3/Overview.bs

@@ -457,6 +457,8 @@ Painting Order and Stacking Contexts</h3>
 		except that their [=positioned=] descendants and any would-be child [=stacking contexts=]
 		take part in the current [=stacking context=].
 
+	Note: The [=root element=] always forms a [=stacking context=] regardless.
+
 	See <a href="https://www.w3.org/TR/CSS2/visuren.html#layers">CSS2 &sect; 9.9 
 	Layered presentation</a>
 	and <a href="https://www.w3.org/TR/CSS2/zindex.html">Appendix E: