[css-align] Add the #flexbox-exception note.

tabatkins · tabatkins · commit 206de7888ae4 · 2017-12-08T16:16:30.000-08:00
diff --git a/css-align-3/Overview.bs b/css-align-3/Overview.bs
@@ -533,6 +533,21 @@ Positional Alignment: the ''center'', ''start'', ''end'', ''self-start'', ''self
 		</figure>
 	</aside>
 
+	<div class=note id=flexbox-exception>
+		For most layout models (block, table, grid, etc),
+		the 'justify-*' properties always align things in the <a>inline axis</a>,
+		while the 'align-*' properties always align things in the <a>block axis</a>.
+
+		Flexbox, on the other hand, has 'justify-*' align things in the <a>main axis</a>
+		and 'align-*' align things in the <a>cross axis</a>.
+		This depends on the value of 'flex-direction':
+		when 'flex-direction' is ''flex-direction/row'' or ''flex-direction/row-reverse'',
+		it matches the other layout modes
+		(<a>inline axis</a> with 'justify-*', <a>block axis</a> with 'align-*');
+		when 'flex-direction' is ''flex-direction/column'' or ''flex-direction/column-reverse'',
+		it has the opposite correspondence.
+	</div>
+
 	<p class='issue'>
 		Make it easier to understand the dual-axis nature of "start" and "end" wrt orthogonal flows.
 
