Make it clearer that auto margins turn off cross-axis alignment.

Author: tabatkins

css3-flexbox/Overview.html

@@ -2639,7 +2639,9 @@ <h3 id=cross-alignment><span class=secno>9.6. </span> Cross-Axis Alignment</h3>
 
    <li id=algo-cross-align> <strong>Align all flex items along the
     cross-axis</strong> per ‘<a href="#flex-item-align"><code
-    class=property>flex-item-align</code></a>’.
+    class=property>flex-item-align</code></a>’, if neither of the item's
+    cross-axis margins are ‘<a href="#flex-item-align-auto"><code
+    class=css>auto</code></a>’.
 
    <li id=algo-cross-container> <strong>Determine the flex container's used
     cross size:</strong>

css3-flexbox/Overview.src.html

@@ -1939,7 +1939,8 @@ <h3 id='cross-alignment'>
 			to the ''auto'' margins.
 
 		<li id='algo-cross-align'>
-			<strong>Align all flex items along the cross-axis</strong> per 'flex-item-align'.
+			<strong>Align all flex items along the cross-axis</strong> per 'flex-item-align',
+			if neither of the item's cross-axis margins are ''auto''.
 
 		<li id='algo-cross-container'>
 			<strong>Determine the flex container's used cross size:</strong>