[css-anchor-position] Clarify that a relpos anchor affects anchor pos, but not a transformed anchor. w3c#10522

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -193,6 +193,21 @@ unless otherwise specified.
 Note: Without this, these [=pseudo-elements=], which are often inaccessible
 by other specifications, cannot be positioned with [=implicit anchor elements=].
 
+### The Anchor's Position ### {#determining-position}
+
+Several features of this specification refer to the position and size of an [=anchor element=].
+The anchor element's position and size is determined after layout,
+and for these purposes
+includes 'position'-based adjustments
+(such as ''position: relative'' or ''position: sticky'').
+
+Post-layout effects, such as 'transform',
+do not affect the [=anchor element's=] "position".
+
+Note: Allowing an anchor to opt into including the effects of 'transform'
+or similar properties
+might be allowed in the future.
+
 <!-- Big Text: a-scope
 
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