[css-conditional-5] Add new named-feature() keywords. w3c#13677 w3c#13678

Author: tabatkins

css-conditional-5/Overview.bs

@@ -212,11 +212,26 @@ At-rules</h4>
 Named features</h4>
 
 	A CSS processor is considered to
-	<dfn export for=CSS id="dfn-support-named-feature" lt="support a named feature|support the named feature">support an named feature</dfn>
+	<dfn export for=CSS id="dfn-support-named-feature" lt="support a named feature|support the named feature">support a named feature</dfn>
 	if it supports the named feature based on the feature definition
 	described in the following list:
 
-	[ No features are currently defined. ]
+	<dl value for="named-feature()" export>
+		: <dfn>anchor-position-follows-transforms</dfn>
+		:: Anchoring to a transformed element automatically takes into account the anchor's transforms,
+			causing the positioned element to shift to match it.
+			[[CSS-ANCHOR-POSITIONING]]
+
+			(An earlier version of the specification did not take transforms into account.)
+	
+		: <dfn>single-axis-scroll-container</dfn>
+		:: The ability to have [=single-axis scroll containers=],
+			where one axis is scrollable and the other is ''overflow/clip''.
+			[[CSS-OVERFLOW-4]]
+
+			(Previously, specifying ''overflow/clip'' alongside a scrollable value caused it to compute to ''overflow/hidden'',
+			which is still a scrollable value even if it doesn't generate a scrollbar.)
+	</dl>
 
 	If the feature is not listed the processor does not support the named feature.