[scroll-animations-1] Mark 'set the offset value' as an abstract-op (#7074)

Author: dontcallmedom

scroll-animations-1/Overview.bs

@@ -400,7 +400,7 @@ The {{EffectTiming/duration}} of a <a>scroll timeline</a> is 100%.
 		offset=]s in the direction specified by {{ScrollTimeline/orientation}} that constitute the
 		equally-distanced in progress intervals in which the timeline is active.
 
-		The procedure to <dfn>set the offset value</dfn> with |val| as the provided
+		The procedure to <dfn abstract-op>set the offset value</dfn> with |val| as the provided
 		value, |pos| as the position in {{ScrollTimeline/scrollOffsets}} and |size|
 		as the {{ScrollTimeline/scrollOffsets}} array size has the following steps: