Clarify containment of a bidi paragraph per <http://lists.w3.org/Archives/Public/www-style/2012Apr/0003.html>.

Author: fantasai

css3-writing-modes/Overview.src.html

@@ -418,9 +418,9 @@ <h3 id="unicode-bidi">
       bidi paragraph immediately contained by the element is determined not
       by the element's computed 'direction' as usual, but by following the
       heuristic in rules P2 and P3 of the Unicode bidirectional algorithm.
-      An element immediately contains a bidi paragraph if it is a block
-      container or bidi-isolating inline and no other such elements intervene
-      between it and the bidi paragraph.
+      An element immediately contains a bidi paragraph if the element itself,
+      but none of its descendants, is a block container or bidi-isolating
+      inline that contains the entire bidi paragraph.
   </dl>
 
   <p class=note>Because the 'unicode-bidi' property does not inherit,