[css-overflow-3] Move note and add subheading

Author: fantasai

css-overflow-3/Overview.bs

@@ -362,7 +362,7 @@ Scrolling Overflow</h3>
 	(For example, in a [=flex container=] it is the [=main-start=] [=cross-start=] corner.)
 	The area beyond the [=scroll origin=] in either axis
 	is considered the <dfn>negative scrollable overflow region</dfn>:
-	content rendered here is the not accessible to the reader,
+	content rendered here is not accessible to the reader,
 	see [[#scrollable]].
 	A [=scroll container=] is said to be scrolled to its [=scroll origin=]
 	when its [=scroll origin=] coincides with the corresponding corner of its [=scrollport=].
@@ -391,6 +391,20 @@ Scrolling Overflow</h3>
 	uses the <a>principal writing mode</a> for determining
 	its [=scroll origin=] and [=initial scroll position=].
 
+	Note: In the case where a [=scroll container=] (or one of its ancestors)
+	is the target of a graphical transform,
+	the UA might need to take this transform into account
+	when mapping user inputs to scrolling operations.
+	For instance, on a touch screen where the user scrolls
+	by directly dragging the content,
+	the transform would be expected to be taken into account
+	to match the direction of scrolling to the gesture.
+	On the other hand, other user inputs
+	(such as the Page Down key, or a 1D scroll wheel)
+	might be more naturally interpreted ignoring the transform.
+	Choosing the appropriate behavior for each scrolling mechanism
+	is the responsibility of the UA.
+
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@@ -407,6 +421,10 @@ Scrolling and Clipping Overflow</h2>
 <h3 id="overflow-control">
 Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3>
 
+	These properties specify whether a box’s [=overflow=] is clipped,
+	and if so,
+	whether it is a [=scroll container=].
+
 	<pre class=propdef>
 		Name: overflow-x, overflow-y, overflow-block, overflow-inline
 		Value: visible | hidden | clip | scroll | auto
@@ -418,10 +436,6 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 		Animation type: discrete
 	</pre>
 
-	These properties specify whether a box’s [=overflow=] is clipped,
-	and if so,
-	whether it is a [=scroll container=].
-
 	The 'overflow-x' property specifies
 	the handling of <a>overflow</a> in the horizontal axis
 	(i.e., overflow from the left and right sides of the box),
@@ -526,6 +540,9 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 	is neither ''overflow/visible'' nor ''overflow/clip'' nor a combination thereof,
 	it [=establishes an independent formatting context=] for its contents.
 
+<h4 id="scroll-visibility">
+Interaction of 'visibility' and 'overflow'</h4>
+
 	If the computed value of the 'visibility' property is ''visibility/hidden''
 	(or ''visibility/collapse'' when it has the same effect as ''visibility/hidden''),
 	and 'overflow' is either ''overflow/scroll'' or ''overflow/auto'',
@@ -543,22 +560,8 @@ Managing Overflow: the 'overflow-x', 'overflow-y', and 'overflow' properties</h3
 		with a descendent of the ''visibility: hidden'' [=scroll container=]
 		that is itself set to ''visibility: visible''.
 
-	Note: In the case where the [=scroll container=] (or one of its ancestors)
-	is the target of a graphical transform,
-	the UA might need to take this transform into account
-	when mapping user inputs to scrolling operations.
-	For instance, on a touch screen where the user scrolls
-	by directly dragging the content,
-	the transform would be expected to be taken into account
-	to match the direction of scrolling to the gesture.
-	On the other hand, other user inputs
-	(such as the Page Down key, or a 1D scroll wheel)
-	might be more naturally interpreted ignoring the transform.
-	Choosing the appropriate behavior for each scrolling mechanism
-	is the responsibility of the UA.
-
-<h3 id="static-media">
-Overflow in Print and Other Static Media</h3>
+<h4 id="static-media">
+Overflow in Print and Other Static Media</h4>
 
 	<p class="advisement">
 		Since scrolling is not possible in static media