diff --git a/css-anchor-1/Overview.bs b/css-anchor-1/Overview.bs
index f10e4b64573..2176c6ce497 100644
--- a/css-anchor-1/Overview.bs
+++ b/css-anchor-1/Overview.bs
@@ -20,6 +20,24 @@ spec:css-position-3;
type:property; text:inset-inline-start
+
+
Introduction {#intro}
=====================
@@ -442,21 +460,40 @@ might not be capable of anchoring the positioned element.
but the details of that will depend on the API assigning them.)
-
+
An element |el| is a acceptable anchor element
for an [=absolutely positioned=] element |query el|
- if all of the following properties apply:
+ if any of the following are true:
+
+ * |query el| is in a higher [=root layer=] than |el|.
+
+ * |query el| and |el| are in the same [=root layer=],
+ and all of the following are true:
+
+ * 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=].
- * 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 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=].
- * If |el| has the same [=containing block=] as |query el|,
- |el| is not [=absolutely positioned=].
+ For the purposes of this algorithm,
+ an element is in a particular root layer
+ corresponding to the closest [=inclusive ancestor=]
+ that is in the [=top layer=],
+ or the document if there isn't one.
+ [=Root layers=] are "higher" if their corresponding element
+ is later in the [=top layer=] list;
+ the layer corresponding to the document is lower than all other layers.
- * 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: This wording around "root layer"
+ needs to live in a stacking-context spec,
+ after pulling the [=top layer=] stuff
+ out of [[fullscreen]].
An element can also have an
implicit anchor element,