[scroll-animations-1] Rewrite to proper algorithmic form

Co-authored-by: Tab Atkins Jr. <jackalmage@gmail.com>

Author: fantasai

scroll-animations-1/Overview.bs

@@ -783,18 +783,26 @@ spec: cssom-view-1; type: dfn;
 		};
 	</pre>
 
-	<dl class=methods dfn-type=method dfn-for="AnimationTimeline">
-		<dt><dfn>getCurrentTime(rangeName)</dfn>
-		<dd>
-			If a rangeName is provided,
-			and is a valid [=named timeline range=] on this {{AnimationTimeline}},
-			returns the percentage progress through that range.
+	<div algorithm="AnimationTimeline.getCurrentTime()">
+		The <code><dfn method for=AnimationTimeline>getCurrentTime(optional |rangeName|)</dfn></code> [=method steps=] are:
 
-			If a rangeName is provided,
-			and is not a valid [=named timeline range=] on this {{AnimationTimeline}},
-			returns null.
+		1. If [=this=] is an [=inactive timeline=],
+			return [=null=].
 
-			If a rangeName is not provided,
-			returns {{AnimationTimeline/currentTime}},
-			representing any time-based value using milliseconds (''ms'').
-	</dl>
+		1. If |rangeName| is provided:
+
+			1. If |rangeName| is a valid [=named timeline range=] on [=this=],
+				let |progress| be the current progress through that range,
+				expressed as a percentage value between 0 and 100.
+
+				Create a [=new unit value=] from (|progress|, "percent")
+				and return it.
+
+			2. Otherwise, return [=null=].
+
+		2. Let |current time| 
+			be the value of [=this's=] {{AnimationTimeline/currentTime}} internal slot.
+
+			Create a [=new unit value=] from (|current time|, "ms")
+			and return it.
+	</div>