[css-lists-3] Add a note pointing at the custom-ident parsing rules for ambiguous grammars. w3c#2624 (comment)

Author: fantasai

css-lists-3/Overview.bs

@@ -521,6 +521,10 @@ Styling Markers: the 'list-style' shorthand property</h3>
 		</pre>
 	</div>
 
+	Note: The <<counter-style>> values of 'list-style-type'
+	can also create grammatical ambiguities.
+	As such values are ultimately <<custom-ident>> values,
+	the parsing rules in [[CSS-VALUES-3]] apply.
 
 	<div class=example highlight=css>
 		Although authors may specify 'list-style' information directly on list item elements