[css-sizing-4] Add an example of width:stretch in a float.

Author: tabatkins

css-sizing-4/Overview.bs

@@ -705,10 +705,28 @@ Stretch-fit Sizing: filling the containing block</h3>
 		</pre>
 	</div>
 
+	<div class="example">
+		Similarly, ''width: stretch'' causes the box to fill its container,
+		being 20px narrower than the width of "some more text"
+		(due to the 10px margin):
+
+		<pre class=html>
+		  &lt;div class="outer">
+		    &lt;div class="inner">text&lt;/div>
+		  &lt;/div>
+		  some more text
+		</pre>
+
+		<pre>
+			.outer { float: left; margin: 0; }
+			.inner { width: stretch; margin: 10px; }
+		</pre>
+	</div>
+
 	<div class="example">
 		On the other hand,
 		in this example the container's height is indefinite,
-		causing a percentage height on the child to [=behave as auto=],
+		which would cause a percentage height on the child to [=behave as auto=],
 		so ''height: stretch'' [=behaves as auto=] as well.
 
 		<pre>