[css-anchor-1] Make anchor-scroll use <anchor-element>, and add 'default' for it to defer to anchor-default.

Author: tabatkins

css-anchor-1/Overview.bs

@@ -417,7 +417,7 @@ Taking Scroll Into Account: the 'anchor-scroll' property {#scroll}
 
 <pre class=propdef>
 Name: anchor-scroll
-Value: none | <<dashed-ident>>
+Value: none | default | <<anchor-element>>
 Initial: none
 Inherited: no
 Applies to: [=absolutely-positioned=] elements
@@ -447,26 +447,21 @@ Its values are:
 	: <dfn>none</dfn>
 	:: No effect.
 
-	: <dfn><<dashed-ident>></dfn>
-	::
-		The scroll offsets of the [=target anchor element=]
-		with the name given by the <<dashed-ident>>
-		will be compensated for in positioning and fallback.
+	: <dfn>default</dfn>
+	:: Behaves as the value of 'anchor-default' on the element.
 
-	: <dfn>implicit</dfn>
+	: <dfn><<anchor-element>></dfn>
 	::
-		The scroll offsets of the [=implicit anchor element=]
-		will be compensated for in positioning and fallback.
+		Selects a [=target anchor element=]
+		the same as ''anchor()'',
+		which will be compensated for in positioning and fallback.
 </dl>
 
 <div algorithm="compensate for scroll">
 	If 'anchor-scroll' is not ''anchor-scroll/none''
 	on an [=absolutely-positioned=] element |query el|,
 	and there is a [=target anchor element=] for |query el|
-	with either the name given by 'anchor-scroll'
-	(if its value is a <<dashed-ident>>)
-	or no name
-	(if its value is ''anchor-scroll/implicit''),
+	given the 'anchor-scroll' value,
 	and at least one ''anchor()'' function on |query el|
 	refers to the same [=target anchor element=],
 	then |query el| has a <dfn>snapshotted scroll offset</dfn>,