[css-scroll-snap] Removed the 'single' value, move and rephrase the issue talking about it.

Author: tabatkins

css-scroll-snap/Overview.bs

@@ -229,7 +229,7 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#snap-type}
 
 	<pre class="propdef">
 	Name: scroll-snap-type
-	Value: none | [ proximity | mandatory ] && single?
+	Value: none | proximity | mandatory
 	Initial: none
 	Applies to: <a>scroll containers</a>
 	Inherited: no
@@ -276,22 +276,21 @@ Scroll Snapping Rules: the 'scroll-snap-type' property {#snap-type}
 			(e.g. content is added, moved, deleted, resized),
 			the scroll offset must be modified to maintain this guarantee.
 
-		<dt><dfn>single</dfn>
-		<dd>
-			This keyword indicates that for <a>inertial scrolls</a>,
-			the next <a>snap position</a> in the direction of the inertia
-			captures all remaining inertia.
-	</dl>
+			Issue: The underlying MS model has a notion of "single mandatory",
+			where the very next snap point automatically absorbs all the inertia,
+			even if a fling would normally take you past two or more snap points.
+			According to Matt, this is actually what MS implemented for ''mandatory''
+			(need to run tests),
+			but it's definitely <em>not</em> what Safari implemented.
+			Do we need a third value to capture this semantic?
+			Useful, for example, to let someone fling through a post they dont' care about
+			and automatically catch the next one
+			in an RSS reader or similar.
 
-	Issue: See <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0452.html">discussion on snapping in response to layout changes</a>.
 
-	Issue: It's not clear from discussions if <css>-ms-scroll-snap-type: mandatory</css> is ''mandatory'' or ''mandatory single''. Should clarify status of the various implementations.
+	</dl>
 
-	Issue: The underlying MS model has the equivalent of "proximity single",
-	but it's not clear from the documentation what it does,
-	and Matt Rakow suggests that it was probably just to complete the 2x2 matrix of values.
-	We should probably instead have "mandatory single" just be a third keyword,
-	perhaps <css>next</css>?
+	Issue: See <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0452.html">discussion on snapping in response to layout changes</a>.
 
 Scroll Snapping Window: the 'scroll-snap-padding' property {#snap-padding}
 -----------------------