[css-overflow] allow line-clamp shorthand syntax to omitting max-lines value

See w3c#9368

Author: frivoal

css-overflow-4/Overview.bs

@@ -816,7 +816,7 @@ Limiting Visible Lines: the 'line-clamp' shorthand property</h3>
 
 	<pre class="propdef shorthand">
 		Name: line-clamp
-		Value: none | <<integer [1,∞]>> <<'block-ellipsis'>>?
+		Value: none | <<integer [1,∞]>>? <<'block-ellipsis'>>?
 		Initial: none
 		Percentages: N/A
 	</pre>
@@ -848,7 +848,8 @@ Limiting Visible Lines: the 'line-clamp' shorthand property</h3>
 			and 'block-ellipsis' to ''block-ellipsis/none''.
 
 		<dt><dfn><<integer [1,∞]>> <'block-ellipsis'>?</dfn>
-		<dd>Sets 'max-lines' to the specified <<integer>>,
+		<dd>Sets 'max-lines' to the specified <<integer>>
+			or to ''max-lines/none'' if omitted,
 			'continue' to ''discard'',
 			and the 'block-ellipsis' property to second component of the value
 			or to ''block-ellipsis/auto'' if omitted.
@@ -2228,6 +2229,8 @@ Recent Changes</h3>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/7144">Issue 7144</a>)
 		<li>Defined [=longhands=] for 'overflow-clip-margin'.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/7245">Issue 7245</a>)
+		<li>Change the 'line-clamp' shorthand syntax to allow omitting the 'max-lines' value
+			(<a href="https://github.com/w3c/csswg-drafts/issues/9368">Issue 9368</a>)
 	</ul>
 
 <h3 id="changes-l3">