[css-overflow-4] Adjust handling of -webkit-box and -webkit-box-orient

See #10324

Author: frivoal

css-overflow-4/Overview.bs

@@ -922,17 +922,11 @@ Legacy compatibility</h4>
 	* it sets 'continue' to ''-webkit-discard'' instead of ''discard''
 	* it unconditionally sets 'block-ellipsis' to ''block-ellipsis/auto''
 
-	Additionally, for children (including anonymous children)
-	of boxes whose 'display' property computes to ''-webkit-box'' or ''-webkit-inline-box'',
-	the used values of the 'max-lines', 'continue', and 'block-ellipsis' properties
-	are taken from the computed values of the parent box;
-	the computed values of these properties on the box itself are ignored.
-
 	The <dfn value for=continue>-webkit-discard</dfn> value behaves identically to ''discard'',
 	except that it only takes effect
-	if the computed value of the 'display' property on the parent
+	if the value of the 'display' property
 	is ''-webkit-box'' or ''-webkit-inline-box''
-	and the computed value of the '-webkit-box-orient' property on the parent
+	and the value of the '-webkit-box-orient' property
 	is ''-webkit-box-orient/vertical''.
 
 	Note: Implementations of the legacy '-webkit-line-clamp' property
@@ -1127,6 +1121,22 @@ Fragmentation of Overflow: the 'continue' property</h3>
 	if it is laid out above the position
 	representing the end of this <a>fragmentation container</a>.
 
+	Additionaliy,
+	for compatibility (see [[#webkit-line-clamp]]),
+	when the [=computed value=] of the 'continue' property is ''discard''
+	and the [=computed value=] of the '-webkit-box-orient' property is ''vertical'':
+	* If the [=computed value=] of the 'display' property is ''-webkit-box'',
+		the box establishes a [=BFC=] as if it had been ''flow-root''.
+	* If the [=computed value=] of the 'display property is ''-webkit-inline-box'',
+		the box establishes a [=BFC=] as if it had been ''inline-block''.
+
+	Note: This means that 'line-clamp' will work
+	if both or neither of ''-webkit-box-orient: vertical''
+	and ''display: -webkit-box'' or ''display: -webkit-inline-box'' are set,
+	but not if ''display: -webkit-box'' or ''display: -webkit-inline-box'' is set
+	while ''-webkit-box-orient: vertical'' isn't,
+	as the box would be a [=flex container=] rather than a [=block container=],
+	and thus the 'continue' property would not apply.
 
 <h2 id=sbg-ext class=nonum>
 Appendix A: Possible extensions for ''scrollbar-gutter''</h2>
@@ -1445,6 +1455,10 @@ Recent Changes</h3>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/9815">Issue 9815</a>)
 		<li>Establish an Independent Formatting Context when ''continue: discard'' is used.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/10323">Issue 10323</a>)
+		<li>Blockify elements with <code>(-webkit-)line-clamp</code>,
+			<code>display: -webkit-(inline-)box</code>
+			and <code>-webkit-box-orient: vertical</code>.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/10324">Issue 10324</a>)
 	</ul>
 
 <h3 id="changes-l3">