[css-overflow-4] Adjust the syntax of the line-clamp property

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>
@@ -847,11 +847,15 @@ Limiting Visible Lines: the 'line-clamp' shorthand property</h3>
 			'continue' to ''continue/auto'',
 			and 'block-ellipsis' to ''block-ellipsis/none''.
 
-		<dt><dfn><<integer [1,∞]>> <'block-ellipsis'>?</dfn>
-		<dd>Sets 'max-lines' to the specified <<integer>>
+		<dt><dfn><<integer [1,∞]>></dfn>
+		</dt><dfn><'block-ellipsis'></dfn>
+		<dd>
+			Sets 'continue' to ''discard''
+			if either or both values ares specified.
+
+			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
+			and 'block-ellipsis' to other component of the value if specified
 			or to ''block-ellipsis/auto'' if omitted.
 
 	</dl>