[css-anchor-1] Anchor names are tree-scoped (but implicit ones dont' necessarily have to be). #7916

Author: tabatkins

css-anchor-1/Overview.bs

@@ -85,6 +85,7 @@ The ''anchor()'' function has three arguments:
 * the <<dashed-ident>> specifies the [=anchor name=] of the [=anchor element=]
 	it will be drawing positioning information from.
 	See [=target anchor element=] for details.
+	This name is a [=tree-scoped reference=].
 
 	If omitted, the function uses an element's [=implicit anchor element=] instead.
 
@@ -298,6 +299,7 @@ Values are defined as follows:
 	:: If the element generates a [=principal box=],
 		the element is an <dfn dfn for local-lt="anchor">anchor element</dfn>,
 		with an <dfn dfn for>anchor name</dfn> equal to the <<dashed-ident>>.
+		The [=anchor name=] is a [=tree-scoped name=].
 
 		Otherwise, the property has no effect.
 </dl>
@@ -311,23 +313,24 @@ might not be capable of anchoring the positioned element.
 <div algorithm>
 	To determine the <dfn>target [=anchor element=]</dfn>
 	given a querying element |query el|
-	and an optional anchor name |name|,
-	find the first element |el| in tree order
-	which satisfies the following conditions:
-
-	* If |name| is not provided,
-		but |query el| has an [=implicit anchor element=],
-		|el| is that element.
-	* If |name| is provided,
-		|el| is an [=anchor element=] with an [=anchor name=] of |name|.
-	* Either |el| is a descendant of |query el|'s [=containing block=],
-		or |query el|'s [=containing block=] is the [=initial containing block=]
-	* If |el| has the same [=containing block=] as |query el|,
-		|el| is not [=absolutely positioned=]
-	* If |el| has a different [=containing block=] from |query el|,
-		the last [=containing block=] in |el|'s [=containing block chain=]
-		before reaching |query el|'s [=containing block=]
-		is not [=absolutely positioned=]
+	and an optional anchor name |name|:
+
+	1. If |name| is not provided:
+		1. If |query el| has an [=implicit anchor element=],
+			return that element.
+		2. Otherwise, return nothing.
+	2. Otherwise, return the first element |el| in tree order
+		that satisfies the following conditions:
+		* |el| and |query el| have the same [=tree/root=].
+		* |el| is an [=anchor element=] with an [=anchor name=] of |name|.
+		* Either |el| is a descendant of |query el|'s [=containing block=],
+			or |query el|'s [=containing block=] is the [=initial containing block=]
+		* If |el| has the same [=containing block=] as |query el|,
+			|el| is not [=absolutely positioned=]
+		* If |el| has a different [=containing block=] from |query el|,
+			the last [=containing block=] in |el|'s [=containing block chain=]
+			before reaching |query el|'s [=containing block=]
+			is not [=absolutely positioned=]
 
 	Note: There might not be any such element.
 
@@ -341,6 +344,12 @@ might not be capable of anchoring the positioned element.
 	into just what's relevant for this purpose,
 	ensuring there is no possibly circularity
 	in anchor positioning.
+
+	Note: Anchor names are scoped to the tree the anchor element is in;
+	if the querying element is in a different [=shadow tree=],
+	they won't find each other.
+	[=Implicit anchor elements=] aren't necessarily limited in the same way,
+	but that might vary depending on the feature assigning the implicit anchor element.
 </div>
 
 An element can also have an <dfn export>implicit anchor element</dfn>,
@@ -356,13 +365,13 @@ potentially different [=implicit anchor elements=] on the same element,
 this specification will define a resolution order.
 
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 Anchor Queries {#queries}