[css-pseudo-4] Clarify that pseudo-elements are suppressed just like regular elements. w3c#625

Author: fantasai

css-pseudo-4/Overview.bs

@@ -1144,6 +1144,10 @@ Generated Content Pseudo-elements: ''::before'' and ''::after''</h3>
   the generated content of ''::before'' and '':after'' pseudo-elements
   can form part of any ''::first-line'' and ''::first-letter'' pseudo-elements
   applied to its <a>originating element</a>.
+  Also as with regular child elements,
+  the ''::before'' and ''::after'' pseudo-elements
+  are suppressed when their parent, the [=originating element=],
+  is [=replaced element|replaced=].
 
 <h3 id="marker-pseudo">
 List Markers: the ''::marker'' pseudo-element</h3>