[css-text-4] Add more notes to 'text-space-collapse: discard' issue.

Author: fantasai

css-text-4/Overview.bs

@@ -2565,7 +2565,9 @@ White Space Collapsing: the 'white-space-collapse' property</h3>
 			This value directs user agents to “discard”
 			all white space in the element.
 
-			Issue: Does this preserve line break opportunities or no? Do we need a "hide" value?
+			Issue: Does this preserve line break opportunities or no? Do we need a distinct "hide" value?
+			If it preserves line break opportunities,
+			maybe it should be replaced with a 'word-boundary-expansion' value?
 	</dl>
 
 	<div class="example">