[css-overflow-3] Better overview definition of what these properties do.

Author: fantasai

css-overflow-3/Overview.bs

@@ -277,6 +277,14 @@ Border box overflow</h3>
 <h2 id="overflow-properties">
 Scrollable Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h2>
 
+	These properties specify whether a box’s content
+	(including any <a>ink overflow</a>)
+	is clipped to its padding edge,
+	and if so,
+	whether it is a <dfn>scrollable box</dfn>
+	that allows the user to scroll clipped parts of its <a>scrollable area</a>
+	into view.
+
 	<pre class=propdef>
 		Name: overflow-x, overflow-y
 		Value: ''visible'' | ''hidden'' | ''clip'' | ''scroll'' | ''auto''
@@ -290,13 +298,11 @@ Scrollable Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</
 	</pre>
 
 	The 'overflow-x' property specifies
-	the handling of <a>scrollable overflow</a> in the horizontal direction
+	the handling of <a>overflow</a> in the horizontal direction
 	(i.e., overflow from the left and right sides of the box),
 	and the 'overflow-y' property specifies the handling
-	of <a>scrollable overflow</a> in the vertical direction
+	of <a>overflow</a> in the vertical direction
 	(i.e., overflow from the top and bottom sides of the box).
-	These properties thereby determine whether or not the box
-	is a <dfn>scrollable box</dfn>.
 
 	<pre class=propdef>
 		Name: overflow