[css-overflow-3] Disable direct interactive scrolling for visibility:…

…hidden

See #4113

css-overflow-3/Overview.bs

@@ -443,6 +443,21 @@ Scrolling and Clipping Overflow: the 'overflow-x', 'overflow-y', and 'overflow'
 	is neither ''overflow/visible'' nor ''overflow/clip'' nor a combination thereof,
 	it [=establishes an independent formatting context=] for its contents.
 
+	If the computed value of the 'visibility' property is ''visibility/hidden''
+	(or ''visibility/collapse'' when it has the same effect as ''visibility/hidden''),
+	and 'overflow' is either ''overflow/scroll'' or ''overflow/auto'',
+	then:
+	* The user agent must not make any scrolling mechanism visible.
+		To the extent that the scrolling mechanism that would normally be visible
+		in the absence of ''visibility: hidden'' affects layout,
+		it continues to do so, but is not painted.
+	* As would be the case with ''overflow: hidden'',
+		scrolling directly triggered by user interactions is disabled,
+		but programmatic scrolling continues to take effect.
+	* The lack of interactive direct scrolling is enforced
+		even if the user interacts (e.g. with a mouse scrolling wheel)
+		with a descendent of the ''visibility: hidden'' [=scroll container=]
+		that is itself set to ''visibility: visible''.
 
 <h3 id="static-media">
 Overflow in Print and Other Static Media</h3>