Clarifying the containing model of positoin sticky.

Author: rossen

css-position/Overview.html

@@ -107,7 +107,7 @@
 
    <h1>CSS Positioned Layout Module Level 3</h1>
 
-   <h2 class="no-num no-toc">Editor's Draft 14 October 2013</h2>
+   <h2 class="no-num no-toc">Editor's Draft 11 November 2013</h2>
 
    <dl>
     <dt>This version:
@@ -1085,10 +1085,12 @@ <h3 id=sticky-positioning><span class=secno>6.2. </span><span
    title="sticky positioning|sticky position|stickily positioned">Sticky
    positioning</span></h3>
 
-  <p id=a-stickily-positioned-box-is-positioned-> A stickily positioned box
-   is positioned similarly to a <a href="#relative-positioning1">relatively
-   positioned</a> box, but the offset is computed with reference to its
-   <span>flow root</span> in addition to the containing block.
+  <p id=a-stickily-positioned-box-is-positioned-> A <span>stickily
+   positioned</span> box is positioned similarly to a <a
+   href="#relative-positioning1">relatively positioned</a> box, but the
+   offset is computed with reference to the nearest ancestor with a
+   <span>scrolling box</span>, or the viewport if no ancestor has a
+   <span>scrolling box</span>.
 
   <p id=specifically-once-a-box-has-been-laid-ou> Specifically, once a box
    has been laid out according to the <a href="#normal-flow0">normal flow</a>