[css-overflow-4] define interaction of line-clamp longhands with balance

See #10827

Author: frivoal

css-overflow-4/Overview.bs

@@ -864,6 +864,11 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 			block-ellipsis-025.html
 		</wpt>
 
+		Displacing content to make room for the [=block overflow ellipsis=]
+		can cause the [=logical height=] of line box where it is inserted to shrink.
+		This must not cause a reevaluation of the effects of the 'continue' property
+		and must not change which line box is the last one before the truncated content.
+
 	* The anonymous inline of [=block overflow ellipsis=] is placed
 		after any remaining content,
 		after [[css-text-4#white-space-phase-2]],
@@ -1402,7 +1407,30 @@ Handling of Excess Content: the 'continue' property</h3>
 
 	</div>
 
-	Additionaliy,
+	When 'text-wrap-style' is set to ''text-wrap-style/balance''
+	on a block container whose 'continue' has a value other than ''continue/auto'',
+	or which participates in the [=block formatting context=]
+	established by an element whose 'continue' has a value other than ''continue/auto'',
+	layout must first be computed as if 'text-wrap-style' were set to 'text-wrap-style/stable'.
+	Then, after any excess content has been truncated
+	and after any necessary [=block overflow ellipsis=] has been inserted,
+	the remaining content must be rebalanced,
+	as per ''text-wrap-style: balance''.
+	If this rebalancing would cause the [=logical height=] of the content to grow,
+	the cutoff point ([=clamp point=] or [=fragmentation break=]) must be reevaluated,
+	and any necessary [=block overflow ellipsis=] reapplied accordingly.
+	Whether to rebalance again after that is up to the user agent,
+	but if it does so,
+	it must always ensure that the constraints
+	about the placement of the cutoff point are adhered to,
+	no matter how many iterations it choose to make.
+
+	For other values of 'text-wrap-style',
+	whether to apply them before the effects of the 'continue' property,
+	after, or both,
+	is undefined in this level.
+
+	Additionally,
 	for compatibility (see [[#webkit-line-clamp]]),
 	when the [=computed value=] of the 'continue' property is ''collapse'', ''continue/-webkit-legacy'', or ''discard''
 	and the [=computed value=] of the '-webkit-box-orient' property is ''vertical'':