[css-overflow-4] blockification of -webkit-box happens at computed value time

See #10435

Author: frivoal

css-overflow-4/Overview.bs

@@ -924,7 +924,7 @@ Legacy compatibility</h4>
 
 	The <dfn value for=continue>-webkit-discard</dfn> value behaves identically to ''discard'',
 	except that it only takes effect
-	if the value of the 'display' property
+	if the [=specified value=] of the 'display' property
 	is ''-webkit-box'' or ''-webkit-inline-box''
 	and the value of the '-webkit-box-orient' property
 	is ''-webkit-box-orient/vertical''.
@@ -1125,9 +1125,11 @@ Fragmentation of Overflow: the 'continue' property</h3>
 	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'',
+	* If the [=specified value=] of the 'display' property is ''-webkit-box'',
+		the [=computed value=] is becomes ''flow-root'' and
+		the box establishes a [=BFC=].
+	* If the [=specified value=] of the 'display property is ''-webkit-inline-box'',
+		the [=computed value=] is becomes ''flow-root'' and
 		the box establishes a [=BFC=] as if it had been ''inline-block''.
 
 	Note: This means that 'line-clamp' will work