[css-scroll-snap] Add scroll-snap-padding (brainstorming here, ignore me, it might make sense when I'm done)

Author: fantasai

css-scroll-snap/Overview.bs

@@ -158,16 +158,16 @@ On the scroll container:
 			<td>High priority
 		<tr>
 			<td>''scroll-snap-destination: <<position>>''
-			<td>''scroll-snap-destination: auto | <<position>>''
-			<td>Keep this property only if needed for compat.
+			<td>''scroll-snap-padding: [ <<length>> | <<percentage> ]{1,4}''
+			<td>
 		<tr>
 			<td>'scroll-snap-points-x'
-			<td>dropped
-			<td>High priority to drop. :)
+			<td>'scroll-snap-points-x'
+			<td>
 		<tr>
 			<td>'scroll-snap-points-y'
-			<td>dropped
-			<td>High priority to drop. :)
+			<td>'scroll-snap-points-y'
+			<td>
 		<tr>
 			<td>n/a
 			<td>''scroll-group-align: [ start | end | edges ]{1,2} | <<position>>#''
@@ -298,6 +298,31 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#snap-type}
 
     Issue: See <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0452.html">discussion on snapping in response to layout</a>.
 
+
+Scroll Snapping Window: the 'scroll-snap-padding' property {#snap-padding}
+-----------------------
+
+
+	<pre class="propdef">
+	Name: scroll-snap-padding
+	Value: [ <<length>> | <<percentage>> ]{1,4}
+	Initial: 0
+	Applies to: <a>scroll containers</a>
+	Inherited: no
+	Percentages: n/a
+	Computed value: as specified
+	Animatable: no
+	Media: interactive
+	</pre>
+
+	The 'scroll-snap-padding' property defines the area of the viewport
+	that is used as the <a>alignment container</a>
+	when aligning <a>scroll snap areas</a> to a <a>snap position</a>.
+	Values are interpreted as for 'padding',
+	and specify inward offsets from each side.
+
+	Issue: Add illustration.
+
 Coordinate-based Snapping {#snap-points}
 =========================
 
@@ -374,11 +399,6 @@ Scroll Snapping Area: the 'scroll-snap-area' property {#the-scroll-snap-area}
 	Specifies the <dfn>scroll snap area</dfn> that is used for snapping this box to the viewport.
 	<<length>> values give outsets (similar to 'margin' or 'border-image-outset').
 
-	Note: This functionality effectively replaces 'scroll-snap-destination',
-	in a way that allows for more control in mixed-content environments
-	(each element can specify its own offsets from the viewport edges)
-	and also plays better with smaller viewports (see [[#small-viewports]]).
-
 Scroll Snapping Alignment: the 'scroll-snap-align' property {#scroll-snap-align}
 --------------------------