[css-text-3] Fix earlier neutral plaintext line wording: bidi switches on paragraph content, not line box content. #4405

Author: fantasai

css-text-3/Overview.bs

@@ -5712,7 +5712,8 @@ Bidirectionality and Line Boxes</h3>
     An empty line box
     (i.e. one that contains no atomic inlines or
      characters other than the line-breaking character, if any)
-    or one that contains only weak or neutral characters,
+    or one whose <a>bidi paragraph</a> has no strong directionality
+    (contains only weak or neutral characters),
     takes its <a>inline base direction</a> from the preceding line box (if any), or,
     if this is the first line box in the containing block,
     then from the 'direction' property of the containing block.