[css-display-3] Clarify that ICB is small viewport size. w3c#6453

Author: fantasai

css-display-3/Overview.bs

@@ -1565,9 +1565,13 @@ Appendix A: Glossary</h2>
 		<dt><dfn>initial containing block</dfn>
 		<dd>
 			The <a>containing block</a> of the [=root element=].
-			The [=initial containing block=] establishes a [=block formatting context=].
-			See <a href="https://www.w3.org/TR/CSS2/visudet.html#containing-block-details">CSS2.1&sect;10.1</a> for [=continuous media=];
-			and [[!CSS-PAGE-3]] for [=paged media=]
+			The [=initial containing block=] establishes a [=block formatting context=],
+			and takes the [=principal writing mode=] of the document
+			(see [[css-writing-modes-4#icb]]).
+			In [=continuous media=],
+			it has the dimensions of the [=small viewport size=]
+			and is anchored at the canvas origin.
+			In [=paged media=], see [[!CSS-PAGE-3]]
 			for its position and dimensions.
 
 		<dt><dfn>formatting context</dfn>
@@ -1934,6 +1938,23 @@ Acknowledgments</h2>
 <h2 class=no-num id="changes">
 Changes</h2>
 
+<h3 id="changes-2020">
+Changes Since 2023 Candidate Recommendation Snapshot</h3>
+
+	<!-- A <a href="https://drafts.csswg.org/css-display-3/issues-cr-2023">Disposition of Comments</a>
+	since the <a href="https://www.w3.org/TR/2023/CR-css-display-3-20230330/">30 March 2023 Candidate Recommendation</a> is available. -->
+
+	Changes since the <a href="https://www.w3.org/TR/2023/CR-css-display-3-20230330/">30 March 2023 Candidate Recommendation Snapshot</a>
+	include:
+
+	<ul>
+		<li id="change-icb-definition">
+			Inlined the CSS2.1 definition of the [=initial containing block=] for [=continuous media=],
+			cross-referenced its [=writing mode=] propagation as defined in [[CSS-WRITING-MODES-4]],
+			and clarified that it refers to the [=small viewport size=].
+			(<a href="https://github.com/w3c/csswg-drafts/issues/6453">Issue 6453</a>)
+	</ul>
+
 <h3 id="changes-2020">
 Changes Since 2020 Candidate Recommendation</h3>