[css-overflow-3] Editorial improvements to end-edge padding clause. #129

Author: fantasai

css-overflow-3/Overview.bs

@@ -265,18 +265,31 @@ Scrollable Overflow</h3>
 			Issue: Need to evaluate compat of honoring or ignoring 'clip' and 'clip-path'.
 
 		<li>
-			Padding on the end-edge sides of the <a>scrollable overflow rectangle</a>
-			representing the end-side padding applied to the <a>scroll container</a>,
-			added such that its content can be scrolled to a position
+			Additional padding added as necessary
+			to the end-side of the [=scrollable overflow rectangle=]
+			such that the box’s content can be scrolled to a position
 			that would satisfy the requirements of ''place-content: end'' alignment.
+
+			Note: This padding represents the box’s own padding
+			within the [=scrollable overflow rectangle=]
+			so that when its in-flow content is scrolled to the end,
+			there is padding between the end-edge of the content
+			and the border edge of the box.
+			It typically ends up being exactly the same size as the box's own padding,
+			except in a few cases, such as when an out-of-flow element,
+			or the visible overflow of a descendent,
+			is increasing the size of the [=scrollable overflow rectangle=].
+
 			Including this padding is optional for <a>block containers</a>
 			in any axis whose corresponding <a>content-distribution property</a>
 			('align-content'/'justify-content')
 			is ''align-content/normal''.
 
-			Issue(129): It's not yet clear if including the end-side padding in the scrollable layer of block containers is Web-compatible, so this clause is under investigation.
-			It appears that Chrome and Safari include such padding <a href="https://bug748518.bmoattachments.org/attachment.cgi?id=618078">in the block axis</a>;
-			and the behavior in the inline axis is <a href="http://jsbin.com/digadoyohi/1/edit?html,css,output">not</a> <a href="http://jsbin.com/vexahocayi/1/edit?html,css,output">clear</a>.
+			Issue(129): It's not yet clear if including the padding here is Web-compatible,
+			so this clause is optional while under investigation.
+			Existing behavior in the inline axis is
+			<a href="http://jsbin.com/digadoyohi/1/edit?html,css,output">not</a>
+			<a href="http://jsbin.com/vexahocayi/1/edit?html,css,output">clear</a>.
 
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