[css-overflow-3] Give corner clipping its own subsection

Author: fantasai

css-overflow-3/Overview.bs

@@ -538,21 +538,6 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 	compute to ''overflow/auto''/''hidden'' (respectively)
 	if one of 'overflow-x' or 'overflow-y' is neither ''visible'' nor ''overflow/clip''.
 
-	As mentioned in [[css-backgrounds-3#corner-clipping]],
-	the clipping region established by 'overflow' can be rounded:
-
-	* When 'overflow-x' and 'overflow-y' compute to
-		''overflow/hidden'', ''overflow/scroll'', or ''overflow/auto'', 
-		the clipping region is rounded
-		based on the border radius,
-		adjusted to the [=padding edge=],
-		as described in [[css-backgrounds-3#corner-shaping]].
-	* When both 'overflow-x' and 'overflow-y' compute to ''overflow/clip'',
-		the clipping region is rounded as described in [[#overflow-clip-margin]].
-	* However, when one of 'overflow-x' or 'overflow-y' computes to ''overflow/clip''
-		and the other computes to ''overflow/visible'',
-		the clipping region is not rounded.
-
 	If the computed value of 'overflow' on a <a>block box</a>
 	is neither ''overflow/visible'' nor ''overflow/clip'' nor a combination thereof,
 	it [=establishes an independent formatting context=] for its contents.
@@ -577,6 +562,24 @@ Interaction of 'visibility' and 'overflow'</h4>
 		with a descendent of the ''visibility: hidden'' [=scroll container=]
 		that is itself set to ''visibility: visible''.
 
+<h4 id="corner-clipping">
+Interaction of 'border-radius' and 'overflow'</h4>
+
+	As mentioned in [[css-backgrounds-3#corner-clipping]],
+	the clipping region established by 'overflow' can be rounded:
+
+	* When 'overflow-x' and 'overflow-y' compute to
+		''overflow/hidden'', ''overflow/scroll'', or ''overflow/auto'',
+		the clipping region is rounded
+		based on the border radius,
+		adjusted to the [=padding edge=],
+		as described in [[css-backgrounds-3#corner-shaping]].
+	* When both 'overflow-x' and 'overflow-y' compute to ''overflow/clip'',
+		the clipping region is rounded as described in [[#overflow-clip-margin]].
+	* However, when one of 'overflow-x' or 'overflow-y' computes to ''overflow/clip''
+		and the other computes to ''overflow/visible'',
+		the clipping region is not rounded.
+
 <h4 id="static-media">
 Overflow in Print and Other Static Media</h4>