[css-scroll-snap-1] Specify which writing mode is used to resolve 'scroll-snap-align' per WG resolution. #3815

Author: fantasai

css-scroll-snap-1/Overview.bs

@@ -644,7 +644,8 @@ Scroll Snapping Alignment: the 'scroll-snap-align' property {#scroll-snap-align}
     its <a>snap area</a> (as the <a>alignment subject</a>)
     within its <a>snap container’s</a> <a>snapport</a> (as the <a>alignment container</a>).
     The two values specify the snapping alignment
-    in the <a>block axis</a> and <a>inline axis</a>, respectively.
+    in the <a>block axis</a> and <a>inline axis</a>, respectively,
+    as determined by the [=snap container=]’s [=writing mode=].
     If only one value is specified, the second value defaults to the same value.
 
     Values are defined as follows:
@@ -676,6 +677,14 @@ Scroll Snapping Alignment: the 'scroll-snap-align' property {#scroll-snap-align}
             in the specified axis.
     </dl>
 
+    Start and end alignments are resolved
+    with respect to the [=writing mode=] of the [=snap container=]
+    unless the [=scroll snap area=] is larger than the [=snapport=],
+    in which case they are resolved with respect to the [=writing mode=] of the box itself.
+    (This allows items in a container to have consistent snap alignment in general,
+    while ensuring that ''scroll-snap-align/start'' always aligns the item
+    to allow reading its contents from the beginning.)
+
 <h4 id="snap-scope">
 Scoping Valid Snap Positions to Visible Boxes</h4>
 
@@ -1188,6 +1197,14 @@ Changes {#changes}
 Changes Since 31 January 2019 CR {#changes-20190131}
 ----------------------------------------------------
 
+	Changes since the <a href="https://www.w3.org/TR/2019/CR-css-scroll-snap-1-20190319/">19 March 2019 Candidate Recommendation</a> include:
+
+	<ul>
+		<li id="change-2019-clarify-writing-mode">
+			Specified which writing mode is used to resolve 'scroll-snap-align'.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3815">Issue 3815</a>)
+	</ul>
+
 	Changes since the <a href="https://www.w3.org/TR/2019/CR-css-scroll-snap-1-20190131/">31 January 2019 Candidate Recommendation</a> include:
 
 	<ul>