[css-values-4] Condition the 'look for local url among the current tree's IDs' for when we're looking for an element. Let other frags act like normal (but stay current-doc, still). w3c#3320

Author: tabatkins

css-values-4/Overview.bs

@@ -33,6 +33,8 @@ spec: cssom-1; type:dfn; text:owner node; for:CSSStyleSheet;
 spec: selectors-4; type: type; text: <q-name>
 spec: infra; type: dfn; text: string;
 spec: css-2023; type: dfn; text: ua
+spec:css-typed-om-1; type:dfn; text:internal representation
+spec:url; type:dfn; text:url; for:/
 </pre>
 <pre class="ignored-specs">
 spec: css-device-adapt-1;
@@ -996,27 +998,28 @@ Fragment URLs</h5>
 	and is a [=tree-scoped reference=]
 	for the URL's [=url/fragment=].
 
-	When matching a <<url>> with the <a>local url flag</a> set,
-	resolve it as a [=tree-scoped reference=]
-	with the tree's IDs as the associated [=tree-scoped names=]:
-	specifically, resolve to the first element
-	in [=tree order=]
-	among the associated [=node tree=]'s descendants
-	with the URL's [=url/fragment=] as its ID.
-	(And, as usual for [=tree-scoped references=],
-	continuing up to the host's tree if needed.)
-	If no such element is found,
-	the URL fails to resolve.
+	When matching a <<url>> with the <a>local url flag</a> set:
+
+	* if the URL's fragment is an element ID reference
+		(rather than, say, a media fragment),
+		resolve it as a [=tree-scoped reference=]
+		with the tree's IDs as the associated [=tree-scoped names=]:
+		specifically, resolve to the first element
+		in [=tree order=]
+		among the associated [=node tree=]'s descendants
+		with the URL's [=url/fragment=] as its ID.
+		(And, as usual for [=tree-scoped references=],
+		continuing up to the host's tree if needed.)
+
+		If no such element is found,
+		the URL fails to resolve.
+
+	* otherwise, resolve the fragment against the current document.
 
 	Issue: Possibly reference <l spec=html>[=find a potential indicated element=]</l>,
 	but that is defined specifically for {{Document}}s,
 	not {{ShadowRoot}}s.
 
-	Issue: I'm just folding together "can't find the ID"
-	and "is a Media Fragment or other non-ID fragment",
-	and treating both of them as a failed reference.
-	I <em>think</em> this is reasonable.
-
 	Note: This means that such fragments will resolve
 	against the contents of the current document
 	(or whichever [=node tree=] the stylesheet lives in,