Added note to flex-order about it not affecting drawing order.

Author: tabatkins

css3-flexbox/Overview.html

@@ -964,7 +964,11 @@ <h3 id=flex-order><span class=secno>3.2. </span> Display Order: the
    href="#flexbox-item"><i>flexbox items</i></a> appear. A flexbox will lay
    out its content starting from the lowest numbered ordinal group and going
    up. Items with the same ordinal group are laid out in the order they
-   appear in the source document.
+   appear in the source document. &lsquo;<a href="#flex-order0"><code
+   class=property>flex-order</code></a>&rsquo; has no effect on
+   stacking/layering; elements must still be drawn over/under each other
+   based on document order, &lsquo;<code
+   class=property>z-index</code>&rsquo;, and other relevant means.
 
   <div class=example>
    <p>The following figure shows a simple tabbed interface, where the tab for

css3-flexbox/Overview.src.html

@@ -435,7 +435,7 @@ <h3 id='flex-order'>
 
 	<p>The 'flex-order' property assigns <i>flexbox items</i> to ordinal groups.</p>
 
-	<p>Ordinal groups control the order in which <i>flexbox items</i> appear.  A flexbox will lay out its content starting from the lowest numbered ordinal group and going up.  Items with the same ordinal group are laid out in the order they appear in the source document.
+	<p>Ordinal groups control the order in which <i>flexbox items</i> appear.  A flexbox will lay out its content starting from the lowest numbered ordinal group and going up.  Items with the same ordinal group are laid out in the order they appear in the source document.  'flex-order' has no effect on stacking/layering; elements must still be drawn over/under each other based on document order, 'z-index', and other relevant means.</p>
 
 	<div class='example'>
 		<p>The following figure shows a simple tabbed interface, where the tab for the active pane is always in front:</p>