[css-lists-3] Require white-space: pre on markers. Allow UA to collapse preserved line breaks. w3c#4448

Author: fantasai

css-lists-3/Overview.bs

@@ -226,6 +226,7 @@ Properties Applying to ''::marker''</h4>
     ::marker, ::before::marker, ::after::marker {
       unicode-bidi: isolate;
       font-variant-numeric: tabular-nums;
+      white-space: pre;
     }
   </pre>
 
@@ -269,6 +270,9 @@ Generating Marker Contents</h3>
 			and ''::marker'' does not generate a box.
 	</dl>
 
+	Additionally, the UA may transform into spaces or discard
+	any preserved [=forced line breaks=].
+
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