Make <container-name> required in the container shorthand

Fixes Issue 7142.

css-contain-3/Overview.bs

@@ -528,13 +528,11 @@ Creating Named Containers: the 'container' shorthand</h3>
 
 	<pre class='propdef shorthand'>
 		Name: container
-		Value: <<'container-name'>>? [ / <<'container-type'>> ]?
+		Value: <<'container-name'>> [ / <<'container-type'>> ]?
 	</pre>
 
 	The 'container' [=shorthand property=] sets
 	both 'container-type' and 'container-name' in the same declaration.
-	If <<'container-name'>> is omitted,
-	it is reset to its [=initial value=].
 	If <<'container-type'>> is omitted,
 	it is reset to its [=initial value=].
 
@@ -1030,6 +1028,8 @@ Changes since the 21 December 2021 First Public Working Draft</h3>
 
 	Significant changes since the <a href="https://www.w3.org/TR/2021/WD-css-contain-3-20211221/">21 December 2021 First Public Working Draft</a> include:
 
+	* Make the <<'container-name'>> in the 'container' shorthand required.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/7142">Issue 7142</a>)
 	* Clarify handling of [=shorthand properties=] in [=container style queries=].
 		(<a href="https://github.com/w3c/csswg-drafts/issues/7095">Issue 7095</a>)
 	* [=Cascade-dependent keywords=] are not allowed as values in a