[css-text] Wording tweak on w3c#4893

Author: frivoal

css-text-3/Overview.bs

@@ -1553,8 +1553,9 @@ Text Processing</h3>
       <li>A sequence at the end of a line
         of <a>collapsible</a> [=spaces=]
         is removed,
-        and any [=collapsible=] trailing U+1680 OGHAM SPACE MARK
-        is also removed.
+        and any trailing U+1680 OGHAM SPACE MARK
+        is also removed
+        if it's 'white-space' property is ''white-space/normal'', ''nowrap'', or ''pre-line''.
 
         <wpt>
           white-space/line-edge-white-space-collapse-001.html