[css-overflow-3] Add example on nesting line-clamp

Author: frivoal

css-overflow-3/Overview.bs

@@ -1042,6 +1042,45 @@ Forcing a Break After a Set Number of Lines: the 'max-lines' property</h3>
 	If fewer than <var>N</var> line boxes exist,
 	then 'max-lines' introduces no <a>region break</a>.
 
+	<div class=example>
+		As ''continue: discard'' does not cause the element to [=establish an independent formatting context=],
+		lines in a nested element with 'line-clamp' are counted,
+		as can be seen in the examples below.
+		<xmp highlight=markup>
+			<div id=a>
+				a: line 1<br>
+				a: line 2<br>
+				<div id=b>
+					b: line 1<br>
+					b: line 2<br>
+					b: line 3<br>
+					b: line 4<br>
+				</div>
+				a: line 3<br>
+				a: line 4<br>
+			</div>
+		</xmp>
+		Sample rendering given <code highlight=css>#a { line-clamp: 5; } b { line-clamp: 2; }</code>:
+		<pre>
+			a: line 1
+			a: line 2
+			b: line 1
+			b: line 2…
+			a: line 3…
+		</pre>
+
+		Sample rendering given <code highlight=css>#a { line-clamp: 3; } b { line-clamp: 2; }</code>:
+		<pre>
+			a: line 1
+			a: line 2
+			b: line 1…
+		</pre>
+		Note that in the second case,
+		the maximum of 2 lines set on element ''#b'' does not take effect,
+		since a forced break is introduced
+		before the second line of this element.
+	</div>
+
 	Note: This implies that 'max-lines' has no effect when applied to [=multi-column containers=],
 	since any line box they contain are nested into [=independent formatting contexts=].