[css-overflow] Handle line breaks in ellipsis

Closes #12557

Author: frivoal

css-overflow-4/Overview.bs

@@ -351,6 +351,11 @@ Inline Overflow Ellipsis: the 'text-overflow' property</h3>
 		<dd>
 			Render the given string to represent clipped inline content.
 
+			All forced line breaks inside the specified string
+			(regardless of 'white-space' value)
+			must be collapsed,
+			as defined for collapsible segment breaks in [[css-text-3#line-break-transform]].
+
 		<dt dfn-type=function><dfn>fade( [ <<length-percentage>> ] )</dfn>
 		<dd>
 			Clip inline content that overflows its line box.
@@ -869,6 +874,12 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 			<wpt>
 				block-ellipsis-024.html
 			</wpt>
+
+			All forced line breaks inside the specified string
+			(regardless of 'white-space' value)
+			must be collapsed,
+			as defined for collapsible segment breaks in [[css-text-3#line-break-transform]].
+
 	</dl>
 
 	When 'block-ellipsis' is neither ''no-ellipsis'' nor the empty string,