[css-overflow-4] continue:discard makes the box establish an IFC

See #10323

css-overflow-4/Overview.bs

@@ -975,45 +975,6 @@ 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=].
 
@@ -1075,15 +1036,15 @@ Fragmentation of Overflow: the 'continue' property</h3>
 
 		<dt><dfn>discard</dfn>
 		<dd>
-			The box becomes a [=fragmentation container=]
+			The box must [=establish an independent formatting context=]
+			and becomes a [=fragmentation container=]
 			that captures <a>region breaks</a>,
 			if it is not already.
 			[[!CSS-BREAK-3]]
 			Content after the first [=region break=] is not rendered (see below).
 			(If the box is a [=multi-column container=],
 			any [=overflow columns=] are also not rendered.)
 
-
 			Note: This [=region break=] might be <a lt="forced break">forced</a>
 			(e.g. imposed by 'max-lines' or by another mechanism,
 			such as the 'break-before'/'break-after' properties)
@@ -1095,8 +1056,6 @@ Fragmentation of Overflow: the 'continue' property</h3>
 			do not cause any content to be discarded.
 	</dl>
 
-	Note: This property does <em>not</em> cause the box to [=establish an independent formatting context=].
-
 	<div class=example>
 		Given an article with one excessively long overflowing line,
 		and four more lines than can fit in the [=fragmentation direction=] as in the illustration bellow,