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

See #10324

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">