[css-multicol-1] Update after i18n WG review

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -333,6 +333,21 @@ The Multi-Column Model</h2>
 	All column boxes in a line have the same column width,
 	and all column boxes in a line have the same column height.
 
+	Note: In text set using a vertical writing mode, 
+	the block direction runs horizontally. 
+	In a vertical writing mode columns are laid out horizontally,
+	and the direction of the flow of blocks may be right to left, or left to right. 
+	The [=column-width=] property therefore refers to the inline size of the column, 
+	and not the physical horizontal width.
+
+	<div class="example">
+		<figure>
+			<img alt="The first image shows horizontal text with a LTR inline direction. The second shows vertical text with blocks flowing right to left. The third shows vertical text with blocks flowing left to right." src="images/writing-modes.svg">
+			<figcaption>A diagram showing the different ways columns may be arranged due to writing mode.
+			<br>From left to right: horizontal-tb, vertical-rl, vertical-lr.</figcaption>
+		</figure>
+	</div>
+
 	Within each [=multicol line=] in the multi-column container,
 	adjacent column boxes are separated by a <dfn noexport>column gap</dfn>,
 	which may contain a <dfn noexport>column rule</dfn>.
@@ -1553,6 +1568,7 @@ This appendix is <em>informative</em>.
 	<li>Added the text, "The margins of two spanners separated only by an absolutely positioned item will collapse with each other, 
 	as absolutely positioned items do not create column boxes." <a href="https://github.com/w3c/csswg-drafts/issues/6265#issuecomment-839909999">Resolved 12 May 2021</a></li>
     <li>Adds an accessibility considerations section. <a href="https://github.com/w3c/csswg-drafts/issues/6283">Request from APA after review.</a></li>
+	<li>Adds a note and example to make clear the manner in which columns are laid out in vertical writing modes. <a href="https://github.com/w3c/csswg-drafts/issues/6301">Request from i18n WG after review.</a></li>
 </ul>
 
 <h3 id="changes-from-20191015">Changes from the <a href="https://www.w3.org/TR/2019/WD-css-multicol-1-20191015/">Working Draft (WD) of 15 October 2019</a></h3>